Skull

SKULL (cranium), i.e., the skeleton of the head of vertebrates, consists of two main parts: the axial skull and the visceral skeleton. The axial skull is a cartilaginous or bony box enclosing and protecting the brain, organ of hearing, and organ of smell, and forming on the sides depressions for the orbits, in which the organ of vision with eye muscles is movably attached. The visceral S. represents the skeleton of the anterior part of the intestine, performing functions of capturing and crushing food (jaws, hyoid apparatus) and respiration (gill apparatus, larynx). The visceral skeleton and its musculature find support on the axial S., with which it enters into close connection. Embryonically, the axial and visceral skeletons of the head develop independently of each other from different sources. The axial S. develops from mesenchyme, the source of which are sclerotomes of the head somites. This mesenchyme concentrates around the anterior end of the notochord, under the base and around the brain, as well as around the already mentioned sense organs (membranous phase of S. development). The formation of cartilaginous tissue begins in the base of the S., on the sides of the notochord ("parachordalia"), and at the base of the forebrain ("cranial trabeculae" or "trabeculae cranii"). Due to the significant bend in the region of the midbrain, the paired trabeculae underlying the forebrain form a significant angle (often close to right) with the parachordalia lying at the base of the hindbrain. As a result, the anterior end of the parachordalia forms a projection directed into the cranial cavity (dorsum sellae). The trabeculae and parachordalia fuse with each other, forming the floor of the cartilaginous S., but between the posterior ends of the trabeculae a membranous space (fenestra basicranialis ant.) is preserved for a long time, in place of which in the adult animal there remains a pit in which the hypophysis lies (sella turcica of the human S.). The lateral parts of the S. are formed by the growth of cartilage upward on the sides of the brain. Sometimes in the orbital area there are also independent centers of chondrification. In addition, in front, around the organ of smell, and on the sides, behind the orbits, around the organ of hearing, cartilaginous capsules develop, which sometimes show certain signs of independence. The roof of the cartilaginous S. is never complete even in lower vertebrates - part of it retains a membranous character (upper fontanelles). In higher vertebrates, cartilage usually develops here only in the occipital region in the form of a bridge connecting the auditory capsules over the medulla oblongata (tectum synoticum). In the vast majority of vertebrates (with the exception of cartilaginous fish), cartilage is partly displaced and partly supplemented by bones, forming together the bony S. In the most ancient fishes and in modern sturgeons there is a continuous external armor of the head from numerous skin bones, which represent the product of the growth of skin scales. Some of these bones grow more significantly, enter into closer connection with the underlying primary S. and form the covering bones of the roof of the S. Typical covering bones of the roof of the S. are as follows: nasal, frontal, pre- and postfrontal, lacrimal and postorbital, supratemporal and squamosal, parietal and postparietal, jugal (nasalia, frontalia, prae-et postfrontalia, lacrimalia, postorbitalia, supratemporalia, squamosa, parietalia, postparietalia, jugalia). In the oral cavity, under the bases of the teeth, also develop superficial ossifications lying in the mucous membrane - covering bones of the floor of the S.: paired vomer and unpaired parasphenoid (vomera, parasphaenoideum), as well as the covering bones of the visceral skeleton. On the other hand, in the walls of the cartilaginous S., bones develop, increasingly displacing cartilage in higher vertebrates. In the occipital region, thus develop: basi-, exo-, and supraoccipital bones (basioccipitale, exoccipitalia, supraoccipitale); in the auditory area: pro-, epi-, and opisthotic bones (prootica, epiotica, opisthotica); in the

Figure 1. Anlage of the axial and visceral skull of a shark embryo: 1- gill arch; 2- hyoid arch; 3- mandibular arch; 4-trabecula; 5- nasal cavity; 6-telencephalon; 7-metencephalon; 8-pleurosphenoid cartilage; 9-cerebellum; 10- trigeminal nerve; 11- facial nerve; 12-medulla oblongata; 13- parachordale; 14- cartilage in the labyrinth capsule; 15- glossopharyngeal nerve; 16- vagus nerve; 17- occipital region; 18- vertebral anlage; 19- spinal ganglion.

orbital area: basi-, pra-, latero-, and orbitosphenoid bones, and in the olfactory area: mes- and exethmoid bones. The visceral skeleton develops from ectodermal mesenchyme, the source of which is at least partially the ganglionic plate. This mesenchyme concentrates in the partitions between successive visceral pouches, as well as

Figure 2. Primary skull of a sturgeon: 1-rostrum; 2- nasal opening; 3-orbit; 4-hyomandibular; 5- gill arch with split upper end; 6-labyrinth capsule; 7- neural arch; 8- chorda; 9- ribs; 10- parabasale; 11- gill arch; 12- copulae; 13- hyoideum; 14- lower jaw; 15- palatoquadrum; 16- symplecticum.

in front of the first pouch in the oral region, forming a series of visceral arches surrounding the head section of the intestine (oral cavity and pharynx) on the sides. These arches chondrify and in doing so break down into several parts each. The anterior arch is called the mandibular arch, the second is the hyoid arch, and the following are the gill arches. The mandibular arch divides into two parts, forming in lower vertebrates the primary upper and lower jaws. The hyoid arch also divides mainly into two parts: the hyomandibular part attached to the auditory capsule of the S., which serves in most fishes as a suspensorium for the jaws, and the lower, proper hyoid (hyoideum). Gill arches as a rule divide into 4 parts each. In higher fishes all these parts ossify.

In the mandibular arch, usually only the posterior parts of the upper part ossify, where the quadrate bone, the posterior pterygoid of fishes, and the epipterygoid of terrestrial vertebrates develop, and the posterior part of the lower part, where the articular bone (articulare) develops. In addition, however, on the mandibular arch, as well as in front of it, a series of covering bones also develop in the mucous membrane. On the lower jaw- dental, splenial, angular, supraangular, dermoarticular (dentale, spleniale, angulare, supraangulare, goniale); on the upper- ecto- and entopterygoid and palatine bones (ecto- et entopterygoideum, palatinum). In front of the mandibular arch in the lips above- maxillary and premaxillary bones (maxilla et praemaxilla) (fig. 1,2,3).

In terrestrial vertebrates, the visceral skeleton undergoes very significant transformations: the upper part of the mandibular arch loses its significance as a S. and becomes part of the palate. The upper jaws are formed entirely from maxilla and praemaxilla. The upper part of the hyoid arch loses its significance as a suspensorium for the jaws and transforms into the auditory ossicle- columella (collumella) of the ear in amphibians, reptiles and birds, or the stapes (stapes) of mammals. In mammals, also the quadrate bone transforms into another auditory ossicle- _Fig. 3. roof of the sturgeon skull: 1- part of the lower jaw-^articulare^ 2-frontal + angular- forms the malleus of the ear (malleus). The angular part of the hyoid arch gives rise to the tympanic membrane of mammals. T. O. in the latter, from the composition of the jaws, a whole series of dermal bones lying in the area

cuium. joints of the lower jaw with the skull (through the intermediary of the quadrate bone), and forms part of the bones of the middle ear. From this it follows that in mammals there is a different articulation of the lower jaw with the skull than in lower vertebrates. The discovery of fossil reptiles occupying to a certain degree an intermediate position (theriodonts) has clarified many details of this process of transformation, as a result of which the lower jaw of mammals consists of only one bone, homologous to the dentary bone (dentale) of reptiles, which has acquired a new, independent articulation with the base of the skull through the progressive development and differentiation of its coronoid process. The lower part of the hyoid arch and one or two gill arches form in terrestrial vertebrates the hyoid bone with its horns. The arches behind are transformed into laryngeal cartilages. The bony skull of fish consists of a very large number of bones forming a more or less complete external armor of the head. The cranial box is relatively small, and the brain occupies only a small part of its cavity. The visceral skeleton forms the greater part of the skull, movably connected with the cranial box. The secondary jaws (maxilla and praemaxilla) are located in the upper lip and often (in bony fish) are movably attached only at their anterior ends to the olfactory region of the skull. The primary upper jaw is also attached to the skull only in front. Behind it is fixed on the auditory capsule mostly only through the intermediary of the upper part of the hyoid arch (hyomandibulare), which forms a suspension for the jaws ('suspensorium'). To the hyoid arch behind are attached the bones of the operculum. The gill arches surround the pharynx and are connected below and in front with the hyoid arch by means of a series of unpaired small bones. All these parts form a movable system participating both in the capture of food and in respiratory movements. In terrestrial vertebrates, as stated, there are very great transformations in the area of the visceral skeleton. The jaw arch articulates with the skull independently ('autostyly'), while the hyoid and gill arches are preserved only in the form of insignificant structures, little connected with the proper skull (hyoid apparatus and laryngeal cartilages). The proper cranial box in the most ancient terrestrial vertebrates (in stegocephalians) was surrounded by just as solid an armor of many dermal bones as in many ancient fish (dermal skull). This external armor supplements the dorsal wall of the brain box (since the primary skeleton here is underdeveloped), and from the latter it extends on the sides. In the space between the cranial box and the external armor is located the chewing musculature. In modern forms this armor is to a large extent reduced - the number of bones is smaller, it loses the character of a continuous covering due to the formation of temporal fossae. Thus, on the sides of the head instead of a continuous covering there is obtained a relatively light frame of bony bridges - temporal arches, strengthening the upper jaw on the axial skull (zygomatic type of skull). In mammals, as in some reptiles, there is only one such 'zygomatic' arch and sometimes in addition an orbito-temporal arch. The bones of the jaw arch, which in many reptiles and birds still form to a certain degree a movable system ('streptostyly'), are now firmly connected with the bones of the axial skull. Especially the epipterygoid completely enters into the composition of the wall of the skull, forming on the sides of the orbital area the bones known under the name of alisphenoids (of mammals), or the great wings of the sphenoid bone of the human skull. The upper jaw bones (maxilla and praemaxilla) are firmly fixed among other bones of the skull, and in monkeys and in man they fuse together with each other. For mammals in general it is rather characteristic the reduction in the number of skull bones by their fusion into some typical complexes. Thus, all 4 occipital bones (exoccipitalia, basi- and supraoccipitale) fuse together into one occipital bone, completely encompassing the foramen magnum and bearing a pair of occipital tubercles for articulation with the spine. With this bone very often fuse also the covering interparietal bones (tabularia and postparietalia of fish and stegocephalians), forming then the 'squama' of the occipital bone. The ossifications of the auditory capsule (prooticum and opisthoticum-mastoideum) fuse into one petrous bone (petrosum), to which in man are also attached the squamous (squamosum) and tympanic (tympanicum), forming the temporal (os temporale) bone of the human skull. In the orbito-temporal area the unpaired basi- and presphenoid fuse with the paired alisphenoid (epipterygoid of reptiles) and orbitosphenoid, forming one sphenoid (os sphenoideum) bone with 'great' and 'small' wings. In higher monkeys and in man with it also fuse the pterygoids. In the olfactory area several ossifications form the ethmoid bone (os ethmoideum) and several olfactory turbinates, attached to the ethmoid (ethmoturbinale), and sometimes also to the nasal (nasoturbinale) and sometimes to the maxillary bone (maxilloturbinale).

Figure 4. Roof of the skull of a stegocephalan: 1-septomaxillare (ha-riale); 2-praemaxillare; 3- maxillare; 4 - praefrontale; 5-lacrimale; 6-frontale; 7~ postorbitale; 8-postfrontale; 9-intertemporale; 10-parie-tale; 11- squamosum; 12- quadratum; 13 - tabulare; 14-postparietale; 15-supra-temporale; 16-jugale.

fusion into some typical complexes. Thus, all 4 occipital bones (exoccipitalia, basi- and supraoccipitale) fuse together into one occipital bone, completely encompassing the foramen magnum and bearing a pair of occipital tubercles for articulation with the spine. With this bone very often fuse also the covering interparietal bones (tabularia and postparietalia of fish and stegocephalians), forming then the 'squama' of the occipital bone. The ossifications of the auditory capsule (prooticum and opisthoticum-mastoideum) fuse into one petrous bone (petrosum), to which in man are also attached the squamous (squamosum) and tympanic (tympanicum), forming the temporal (os temporale) bone of the human skull. In the orbito-temporal area the unpaired basi- and presphenoid fuse with the paired alisphenoid (epipterygoid of reptiles) and orbitosphenoid, forming one sphenoid (os sphenoideum) bone with 'great' and 'small' wings. In higher monkeys and in man with it also fuse the pterygoids. In the olfactory area several ossifications form the ethmoid bone (os ethmoideum) and several olfactory turbinates, attached to the ethmoid (ethmoturbinale), and sometimes also to the nasal (nasoturbinale) and sometimes to the maxillary bone (maxilloturbinale).

The floor of the skull, in fish and lower terrestrial vertebrates lined with a long unpaired parasphenoid and paired vomers, forms together with the bones of the upper part of the jaw arch a support for the roof of the oral cavity, so-called primary hard palate, bounded on the outside by the maxillary and premaxillary bones. Both pairs of nostrils are located in fish outside the oral cavity, usually on the dorsal part of the olfactory area of the head. Only in dipnoans they lie under the upper lip. In amphibians and lower reptiles the pair of 'internal' nostrils or primary choanae open at the anterior edge of the palate between the maxillary bones and the vomer. In some reptiles from the maxillary bones develop horizontal outgrowths, shutting off some space under the olfactory area of the skull, where the choanae open. These outgrowths form the rudiment of a secondary hard palate, which separates the upper respiratory part of the oral cavity (ductus nasopharyngeus). The vomers fuse together and form a septum dividing this cavity. Behind the secondary palate it opens by means of 'secondary choanae'. Part of the primary choanae, connected with the Jacobson's organ, is preserved in the form of 'foramina incisiva'. With further development of the secondary hard palate into its composition also enter the palatal processes of the palatine bones, and sometimes also the pterygoid bones (crocodiles, whales), usually bounding the secondary choanae on the sides * The skull of mammals has a rather characteristic general appearance. The jaws are relatively high, the base of the skull is wide and the orbits are Figure 5. Skull of a lizard from below: 1- choanae; 2 -lateral window (roof of the palate); 3- interpterygoid fissure; 4-pterygoid; 5 - proc. paroticus; 6-basipterygoid joint; 7-quadratum; 8-proc. cultriformis;.9-transversum; 10-palatinum; 11-vo-mer.

Figure 6. Skull of a primitive reptile (tuatara) with two zygomatic arches, from the side: 2- frontale; 2-postfrontale; 3-parietale; 4-squamosum; 5-pterygoid; 6-quadrat. jugale; 7 - jugale; 8-epipterygoid; 9-sept, interorbitale (unossified); 10 - maxill.

widened (no interorbital septum). It is also characteristic the rather considerable growth of the cranial cavity, thanks to which the skull behind the orbits acquires a rounded shape, as well as the growth of the olfactory area. For monkeys, and especially for man, on the contrary, is characteristic the reduction in size of the olfactory part, but all the more considerable development of the cranial box, which advances from above onto the orbits and onto the olfactory area, so that the ethmoid plate becomes more and more inclined, finally taking in man a horizontal position. The jaws are reduced, and the axis passing through the facial parts becomes in man perpendicular to the axis passing along the base of the skull (fig. 4-9).

I. Shmal'gauzen.

The skull in an anthropological respect. For man in comparison with all other animals is characteristic the considerable development of the cerebral part of the skull (neurocranium) and the reduction of its facial part (splanchnocranium). According to the data of Hoor in a median-sagittal section the area of the face in man constitutes 25-45% of the cerebral, whereas in the most man-like monkey-chimpanzee - this ratio reaches 100-130 %. The capacity of the cranial cavity (cavum cranii) of adult humans varies approximately from 1,000 to 2,000 cm³, in most cases it approaches 1350-1550 cm*. The capacit

" " bone of the skull in anthropomorphic forms is much lower: for male gorillas on average about 500 cm³, for orangutans and chimpanzees even less. The large size of the brain is associated with a number of important morphological features of the human skull: strong development in height and rounding of the vault; very large parietal bones; protruding frontal section, extending downward over the face; oblique, rather than vertical as in other mammals, position of the occipital bone scale; pronounced downward bend of the base. The reduction of the visceral (facial) part of the skull is explained primarily by the far-reaching reduction of the chewing apparatus. Reduction

Figure 7. Skull of a mammal (dog) from below: 1 - praemaxillare; 2-for. inci-sivum; 3-maxillare; 4- pa-latinum; 5-choanae; 6-for. sup.; 8 - jugale; 9 - for. turidum; 10 -for. ovale; 11 - squamosum; 12 - auditory opening; 13-for. lacerum post.; 14^ tor. condyloid. (hypoglossus); 15 - condyl. occipit.; 16-for. occipitale; 17-bulla tympani; 18-basi-occipit.; 19-for. lacerum ant.; 20-sphenoid; 21 - pterygoid.

this is manifested in the relatively small size of the teeth, not separated by gaps (diastemas), in the shortening and widening of the palatal arch, in the less spread apart than in anthropomorphic forms, position of the zygomatic bones, in the slight forward projection of the upper jaw, in the weak development of the external bone relief, in particular in the absence of the sagittal crest, so typical for male gorillas, orangutans and partially chimpanzees. Many characteristic human features in the structure of the skull, especially its base, are connected with upright posture and the vertical direction of the longitudinal axis

Figure 8. Diagrams of the relationships of the jaw joint and auditory ossicles in reptiles: 1-dentale; 2-coronoid.; 3-quadratum; 4-proc. dorsalis; 5-proc. paroticus; 6-stapes; 7-extracolumella; 8- hyoideum; 9 - goniale; 10-arti- culare; 11-angulare; 12-suprangulare.

Figure 9. Diagram of the relationships of the jaw joint and auditory ossicles in mammals: 1-dentale; 2-cart. Meckeli; 3-proc. articularis; 4-malleus (articulare); 5- incus (quadratum); 6-stapes; 7-hyoideum; 8-tympanicum (angulare); 9- proc. folianus (goniale).

body. These include: the central location of the foramen magnum, which is shifted forward and tilted from front to back rather than backward as in all other mammals; the intensive development of the mastoid and styloid processes; and the weakening of the muscular relief of the occiput, manifested in the disappearance of the transverse occipital crest. Other specific features of the human skull that should be noted include: the comparatively small thickness of the bones and the resulting more complete correspondence between the external shape of the skull and the brain capsule than in other higher primates; the relatively weak prominence of the superciliary arches; the bony nose protruding from the plane of the face; the so-called "anthropine" shape of the lower margin of the piriform aperture, expressed in a sharp boundary between the entrance to the nasal cavity and the upper jaw; and the presence of a developed mental eminence. Along with these differences, the human skull reveals many common features with the skulls of other primates, especially with the skulls of Old World narrow-nosed monkeys (ossifying external auditory meatus, absence of contact between the zygomatic and parietal bones in the lateral wall of the skull, absence of the third premolar tooth, etc.). From a phylogenetic standpoint, analogies with African anthropoid primates, traceable through a number of secondary, evolutionarily indifferent features of the skull, are of particular interest. Thus, unlike the Asian anthropoids—the gibbon and the orangutan—man, the gorilla, and the chimpanzee are characterized by the presence of frontal sinuses and a wide interorbital space (Weinert). Specifically, man approaches the chimpanzee in the shape and size of the frontal sinuses, in the ratio of the internal and external length of the skull, in the early disappearance of the intermaxillary bone in the process of ontogeny, and in the very frequent (90-100%) presence of the foramen spinosum at the base of the skull. A comparison of data from comparative anatomy, embryology, and paleoanthropology makes it possible to outline the main pathways of the phylogeny of the human skull. In the process of anthropogenesis, there undoubtedly occurred: an increase in the total capacity of the skull, an increase in its height, a broadening and shifting forward of the frontal region over the visceral part, the development of the mental eminence, the formation of a forward-projecting bony nose, a general gracilization of the entire appearance of the skull, in particular a reduction in bone thickness, a weakening of prognathism (protrusion of the jaws), and a reduction of the brow ridges and occipital relief. It is highly probable that in the course of skull evolution, the transverse dimensions of the brain capsule increased somewhat faster than the longitudinal ones; the consequence of this was the gradual brachycephalization of mankind (see Brachycephaly). The skulls of fossil species and genera of the family Hominidae—Pithecanthropus, Sinanthropus, Neanderthal man—occupy a position intermediate between anthropoid apes and modern humans in many features (capacity, vault height, chin, relief, etc.). The skull structure characteristic of an adult human develops gradually in ontogeny. The primary membranous (primordial) skull of a human is indistinguishable from that of an ape. By the time of birth, the capacity of the brain capsule reaches 350-400 cm³ (about 25% of the adult capacity). The skull of the newborn and infant is also characterized by: very small dimensions of the facial part compared to the cerebral part (about 18%), thin bones, almost complete absence of muscular relief, in particular the brow ridges, the presence of unossified connective tissue areas (fontanelles), relatively weak development of the base, a pentagonal shape when viewed from above, small protrusion of the bony nose and chin, the presence of the frontal suture, and so on. Further growth of the skull parts is uneven—the visceral part increases both absolutely and relatively much faster than the cerebral part. The growth of the skull is most intense during the first year of life, when its length increases by 12 mm and its width by 14 mm. By the 12th year, the annual growth of both dimensions drops to 1 mm. From 28-30 years of age, the closure (obliteration) of the sutures between individual skull bones begins. In old age, a reduction of the alveolar parts of the jaws occurs, associated with the loss of teeth. Various disruptions in the normal course of ontogeny lead to the appearance of anomalous and pathological forms of the skull. These include, for example, microcephaly, macrocephaly, and oxycephaly (see). A number of anomalies are caused by the premature obliteration of sutures and the resulting compensatory growth of the cranial cavity in one direction. Early closure of the coronal suture leads to a tower-like shape of the skull, and of the sagittal suture to an extremely elongated "scaphoid" shape (scaphocephaly). One-sided arrest of growth entails the formation of a sharply asymmetrical "skew" skull (plagiocephaly). Artificial deformations of the skull depend mainly on the action of various mechanical factors on the plastic head of the child, caused by the design of the cradle, methods of swaddling and carrying small children, and so on. Sexual differences in the skull are less sharply expressed in humans than in other higher primates. The female skull is smaller than the male in absolute dimensions, but larger in relation to body height and weight. Compared to the male, the woman also has thinner bones, weaker muscular relief on them, a straighter forehead, somewhat less prominent nose and chin, and rounder orbits. These differences are far from absolute and are clearly revealed only in summary comparisons of cranial series belonging to different sexes. The study of racial variations of the skull is of great anthropological importance. In the works of the 19th and early 20th centuries, the greatest attention was paid to comparing various cranial indices characterizing cranial series belonging to individual modern or ancient ethnic groups of mankind. The most widespread of these indices was the so-called "cephalic" (on the living) or "cranial" (on the skull) index, proposed by the Swedish anatomist Anders Retzius, which gives the ratio of the greatest (parietal) width of the skull to its greatest length. Excessive enthusiasm for indices led craniometry (see) to detach itself from other research methods and gave it a formalist imprint. At the present time, leading anthropologists of the USSR, Western Europe, and America take into account in racial analysis not only indices, but also absolute values of cranial diameters and angles, as well as qualitative "descriptive" features that do not lend themselves to measurement (e.g., the degree of development of the brow ridges, the depth of the canine fossa, the general contour in norma verticalis, etc.). Differences between the skulls of the main human races proceed predominantly along the lines of secondary features that do not have great evolutionary significance and do not provide a basis for conclusions about the morphological primitiveness of one or another of the currently living varieties of mankind. If these differences do embrace essential evolutionary features, the distribution of "primitive" and "progressive" forms among individual races turns out to be so motley that, based on the totality of skull features, none of them can be placed "higher" or "lower" than another. For example, according to the degree of jaw protrusion, negroids (the "black" race) are more "primitive" than europeoids (the "whites"); according to forehead slope and brow ridge development, there is a diametrically opposite relationship. Also devoid of any scientific foundation are the constructions of Günther, Lenz, Walther Darré, and others, popular in fascist Germany, concerning the connection of racial features of the skull (first of all, the cephalic index) with certain psychological qualities. I. Cheboksarov. In humans, two groups of skull bones are distinguished: the bones of the cranial vault (ossa cranii) and the facial bones (ossa faciei). The former include: the occipital bone (os occipitale), sphenoid bone (os sphenoidale), temporal bones (ossa temporalia), parietal bones (ossa parietalia), frontal bone (os frontale), and ethmoid bone (os ethmoidale). The facial bones include: the nasal bones (ossa nasalia), lacrimal bones (ossa lacrimalia), vomer (vomer), inferior nasal conchae (conchae nasales inferiores), maxillary bones (maxillae), palatine bones (ossa palatina), zygomatic bones (ossa zygomatica), mandible (mandibula), and hyoid bone (os hyoideum). The connections of these bones are extremely diverse; all of them, with the exception of the mandible and the hyoid bone, are immobile. The shape of the skeleton of the head is determined by the ratio of the vertical, transverse, and longitudinal diameters and the deviation between the cerebral and facial skull. The head rests with all its weight on the spine, with which it articulates in the atlanto-occipital articulation. On the skull, the vault and the base are distinguished. The former, corresponding to the convex external surface (fornix cranii externus), has a concave internal surface (fornix cranii internus). The base of the skull, consisting of massive, irregularly shaped bones, also has an internal surface (basis cranii interna) and an external one (basis cranii externa). The border between the vault and the base of the skull runs from the external occipital protuberance on both sides to the asterion, from here to the squamosomastoid suture and the crest of the zygomatic process of the temporal bone.

It passes the tuberculum articulare and along the crista infraorbitalis reaches the sutura spheno-zygomatica; further, it runs along the edge of the greater wing of the sphenoid bone, which bounds the fissura orbitalis from above and laterally, approaches the body of the sphenoid bone, whence, running anterior to the base of the pterygoid process, it reaches the rostrum sphenoidale on both sides. Ontogeny. In the first week of development, there is only the germinal vesicle. On the 20th week, the rudiments of the nervous system and blood vessels begin to form, the amniotic fold and the primary segment arise. The head region separates. At the end of the 1st month, there are rudiments of the eyes and ear in the form of a small protrusion of the head region. Very sharp proportions: the head is almost half the body length due to the powerful development of the brain. The neck is absent. In the 2nd month, the rate of development slows down, brain flexures are noticed; the cerebral hemispheres bend backward. The face begins to be designated in the 2nd half of the 2nd month in a 15 mm embryo; in an 18 mm long embryo, the nose is clearly visible. In the 2nd month, the auricle begins to straighten. The head begins to straighten, the cerebral skull is still large. The protrusions of individual parts of the skull cease to be visible upon external inspection. By the end of the 3rd month, the detailing of the head shapes is not yet completed. The cerebellum still forms a protrusion. The cerebral hemispheres approach backward. The brain of a newborn resembles that of an adult in appearance. Subsequently, the details of the internal structure are developed. The skull develops from mesenchyme. The bones of the head skeleton arise: 1) from the cartilaginous primordial skull, 2) from the cartilaginous skeleton of the branchial arch, 3) from the skin-mucous region. The vault of the skull consists of 3 regions. 1. Regio fronto-parieto-occipitalis; boundaries: anteriorly—the upper orbital margin, posteriorly—the superior nuchal line, laterally—the superior semicircular line of the parietal bones. 2. Regio temporalis—the lateral sections between the superior semicircular line of the parietal bones and the zygomatic arch with a continuation to the mastoid notch. 3. To the vault, for practical reasons, Kupiyanov also attaches the regio mastoidea. The skeleton of the regio fronto-parieto-occipitalis includes the squama of the frontal bone, the medial parts of both parietal bones, and the squama of the occipital bone. The squamous part constitutes the main part of the frontal bone. It adjoins both parietal bones with its parietal margin by means of the coronal suture and with the sphenoid margin (sutura spheno-frontalis) to the greater wing of the sphenoid bone. The outer surface is convex, with a tuber (tuber frontale) on each side. Above the orbital margins are the superciliary arches (arcus superciliares), between them is the glabella (glabella). On the upper orbital margin, in its inner half, there are two notches: medially the frontal notch, laterally the supraorbital notch; instead of the latter, there is sometimes a supraorbital foramen. The inner surface is smooth, mostly having digital impressions and cerebral ridges, as well as Pacchionian granulations. Parietal bones—see Parietal bone. The squamous part constitutes the greater part of the occipital bone; it is flat, concave on the inside, convex on the outside, and has a triangular shape; by means of the occipitomastoid suture, it is separated from the mastoid part of the temporal bone, and by means of the lambdoid suture—from both parietals. On the inner (cerebral) surface of the squamous bone, there is a cruciform eminence (eminentia cruciata), the upper and lateral limbs of which are formed by sulci, while the lower limb is formed by a crest extending to the posterior circumference of the foramen magnum. In these sulci lie the venous sinuses of the dura mater. In the middle of the cruciform eminence is the internal occipital protuberance (protuberantia occipitalis interna). The outer surface of the squama of the occipital bone is divided by the superior nuchal lines extending from the external occipital protuberance into two parts: the upper, relatively smooth triangular part (planum occipitale) and the lower rough part (planum nuchale). But above the superior nuchal lines directed toward the mastoid margin, there are often arcuate curved highest nuchal lines. From the external occipital protuberance, the occipital crest runs to the posterior circumference of the foramen magnum; from its middle, parallel to the superior nuchal lines, run the inferior nuchal lines. The bones of the skull vault consist of two plates—the external lamina and internal lamina, between which is enclosed the diploe, spongy substance, and the diploe is expressed differently in various areas, which explains the unequal thickness of the bone wall. The outer plate is thicker and stronger than the inner one, which explains why the inner plate also bears another name—vitreous lamina. Regio temporalis. On the skeleton of this region, the temporal plane is expressed, composed of the squama of the temporal bone, the greater wings of the sphenoid, part of the parietal and the frontal process of the zygomatic bone and the zygomatic process of the frontal; by the infratemporal crest, this area is separated from the infratemporal plane. This area is placed obliquely with respect to the base of the skull, as a result of which a space called the temporal fossa is formed between it and the zygomatic arch. Below the crest there is also a depression—the infratemporal fossa, which appears as if a continuation of the temporal fossa; it communicates with the sphenomaxillary fossa, pterygopalatine fossa, and the orbit, which explains the spread of abscesses. The bone consists of three layers: the outer and inner plates and the spongy substance between them, but the latter is insignificantly expressed, as a result of which the bone is thinned and of all parts of the skull is the least stable. Regio mastoidea corresponds to the zygomatic process. The surface is rough, in its middle there is a rather smooth area (Chipault's triangle), bounded above by the continuation of the root of the zygomatic arch, posteriorly by the mastoid crest, anteriorly by the upper-posterior segment of the circumference of the external acoustic meatus. The practical significance of the triangle is that surgical interventions are performed within its limits. The external base of the skull has two parts—anterior and posterior. Within the anterior part are enclosed: the body of the sphenoid bone, the basilar process of the occipital, the lower surfaces of the greater wings of the sphenoid bone, and part of the temporal. This part has a series of apertures through which vessels and nerves pass. Anterior to the lateral crest (its beginning is the external plate of the pterygoid process, extending then to the styloid process and mastoid process) lies the foramen ovale, medially at 0.5 cm is the internal carotid foramen and foramen lacerum. Anteriorly and laterally to the base of the angular spine lies the spinosus foramen, medially—the musculotubular canal; on the medial side of the crest lie the external carotid pore and jugular foramen; finally, the stylomastoid foramen lies behind the styloid process. The area enclosed between the lateral crests is called the hilus, and its middle part is the guttural fossa, since it forms the roof of the nasopharynx. Medial to the infratemporal fossa lies the pterygopalatine fossa; there is no lateral wall, but there is a fissure communicating both adjacent fossae. The pterygopalatine fossa passes into a canal (pterygopalatine canal) which opens on the lower surface of the hard palate; by means of the sphenopalatine foramen there is communication with the nasal cavity. By means of the foramen rotundum, the pterygoid fossa communicates with the middle cranial fossa, through the inferior orbital fissure—with the orbit. The internal base of the skull consists of three processes—anterior, middle, and posterior. The anterior part is limited by the edge of the lesser wings of the sphenoid bone and the anterior crest of the sella turcica. The middle cranial fossa is limited anteriorly by the edge of the lesser wings of the sphenoid bone and the sphenoidal limbus, posteriorly—by the upper edge of the pyramid of the temporal bone and the wall of the sella turcica. In the middle part are located the optic foramen (ophthalmic artery and optic nerve), superior orbital fissure [oculomotor, trochlear, abducens, and ophthalmic nerves (first branch of the trigeminal)], foramen rotundum [maxillary nerve (second branch of the trigeminal)], foramen ovale [mandibular nerve (third branch of the trigeminal)], spinosus foramen (middle meningeal artery), anterior lacerum foramen (superficial petrosal nerve). The posterior cranial fossa is anteriorly bounded by the superior crest of the pyramids and the dorsum sellae, and posteriorly—by the horizontal branch of the internal cruciform eminence of the occipital bone; in the center is located the foramen magnum, through which the medulla oblongata passes with arteries. On the posterior surface of the pyramid lies the internal acoustic meatus (facial and acoustic nerves); besides, there are the following apertures: posterior lacerum foramen (9th, 10th, 11th pairs of cranial nerves, jugular vein, posterior meningeal artery), anterior condylar foramen (hypoglossal nerve and vein), mastoid foramen. Soft tissues by regions are arranged as follows. In the regio fronto-parieto-occipitalis, the skin is of considerable thickness, largely covered with hair, contains a large amount of sebaceous glands; the subcutaneous adipose tissue is penetrated by a series of fibrous partitions that very firmly connect the skin with the deeper tendon-muscle layer.

Next goes the galea aponeurotica, a tendinous expansion common to both the frontal muscle and the occipital muscle. In front, it begins from the superciliary arches, the frontal process of the maxilla, and the root of the nose; behind, on the squama of the occipital bone, above the superior nuchal line. The upper surface of the aponeurosis connects with the previous layer by connective tissue bridges; the lower surface

Figure 10. Vessels and nerves of the head from the side: 1 - greater occipital nerve; 2 - occipital artery; 3 - lesser occipital nerve; 4 - posterior auricular branch of the facial nerve; 5 - sternocleidomastoid muscle; 6 - facial nerve; 7 - superficial temporal artery and vein; 8 - auriculotemporal nerve; 9 - frontal branch of the superficial temporal artery; 10 - lacrimal nerve; 11 - supraorbital nerve; 12 - supraorbital artery; 13 - parietal branch of the superficial temporal artery.

lies against loose cellular tissue, passes laterally into the temporal region, and is lost in the cellular tissue of the cheek. Subaponeurotic cellular tissue is especially pronounced in the vault. Finally comes the periosteum, loosely connected to the bone except at the suture sites. In the temporal region, the soft tissues have the following layers: thin skin, less durable, connected to a layer of fat beneath which lies the superficial fascia, essentially a thinned continuation of the galea aponeurotica; next goes the temporal fascia, a strong temporal aponeurosis. The subperiosteal layer is very weakly expressed, and the periosteum directly adjoins the bone. There is a fairly developed vascular network on the head; the main arterial trunks are: the supraorbital artery, frontal artery, superficial temporal artery, posterior auricular artery, and occipital artery; these vessels are located in the frontoparietooccipital region, while the superficial temporal artery is in the temporal region (Figures 10–12). The venous system is arranged in three tiers: skin veins, diploic veins, sinuses. - Nervous system. Nerves accompany the arteries (frontal nerve, auriculotemporal nerve, supraorbital nerve, anterior and posterior deep temporal nerves). - Lymphatic vessels gather into several groups of lymph glands: 1) in the region of the parotid gland - collecting lymph from the anterior section of the region; 2) behind and below the angle of the auricle is another group of glands, and finally 3) the third group of glands is located at the attachment site of the trapezius muscle (Figure 13). The cranial cavity accommodates the brain with its membranes and vessels, wherein the frontal lobes of the brain are located in the anterior cranial fossa of the internal base of the skull, the temporal lobes in the middle, and the cerebellum, medulla oblongata, nerve origins, and vessels in the posterior. The type of skull is determined by the ratio of the transverse and longitudinal diameters. The transverse size is taken at the level of the parietal tuberosities, and the longitudinal between the external occipital protuberance and the glabella. To calculate the cranial index, the length is taken as 100, and the width is expressed as a percentage, and thus the calculation is made according to the formula: width × 100 / length. Skulls are distinguished as long-headed (dolichocephals), whose index is 74.9 and less; medium-headed (mesocephals) with an index from 75.0 to 79.9; round-headed (brachycephals) with an index of 80.0 and higher. The height index is calculated...

by the formula: height × 100 / length; skull height is the vertical dimension from the basion (anterior middle point of the foramen magnum) to the vertex. With an index above 75.0, the skull is high (hypsicephal); 70.0–75.0, orthocephal; below 70.0, platycephal. In addition, when determining the type of skull, one should take into account where its main mass is directed: toward the frontal or occipital region, with the linea biauricularis serving as the reference point—a vertical line connecting the external auditory meatuses. If the main mass of the cerebral skull is located in front of this line, the skull is called frontipetal, and if behind, occipitopetal. Skull types are of great importance, because various types of its contents correspond to these types: for example, in dolichocephals the base

Figure 11. Vessels and nerves of the occipital region: 1 - occipital muscle; 2 - greater occipital nerve; 3 - occipital artery; 4 - lesser occipital nerve; 5 - posterior trunks of the cervical nerves; 6 - trapezius muscle; 7 - sternocleidomastoid muscle; 8 - splenius muscle; 9 - attachment of the trapezius muscle to the superior nuchal line; 10 - posterior auricular artery.

of the skull is elongated in length, and accordingly there is a displacement of the openings for vessels and nerves. Developmental defects of the skull bones are quite common, but the practical significance is mainly held by partial underdevelopment of the skull bones, leading to the formation of so-called cerebral hernias; among other irregularities of the cranial bones, aplasia cranii should be noted, which is manifested by a deficiency in the ossification of the cranial bones. Rickets is considered the cause of such an anomaly. Treatment boils down to enhanced

Figure 12. Vessels and nerves of the frontal region: 1 - parietal branch of the superficial temporal artery; 2 - frontal branch of the superficial temporal artery; 3 - lacrimal nerve; 4 - superficial temporal artery; 5 - infratrochlear nerve; 6 - angular artery; 7 - inferior palpebral arch; 8 - superior palpebral arch; 9 - lacrimal nerve; 10 - supratrochlear nerve; 11 - frontal nerve and frontal artery; 12 - supraorbital artery and nerve; 13 - frontal muscle.

nutrition of such children. The reverse and in all respects more important clinical form is premature ossification of the cranial bones, leading to insufficient capacity of the cranial cavity with subsequent arrest of brain development—microcephaly (see). Congenital clefts of the skull cause herniated protrusions of the cranial contents through a defect in the skull bones. Anterior and posterior hernias are distinguished. Anterior ones are located along the line connecting the facial bones with the cranial bones. Depending on the direction of the hernia canal, frontonasal, frontoethmoidal, and frontoorbital hernias are distinguished among anterior hernias. Posterior hernias are located strictly along the midline of the skull, above or below the occipital protuberance. Depending on the nature of the hernia contents, they are divided into encephalocele, if the contents consist of brain tissue; hydrencephalocele, when there is a cavity among the brain tissue containing cerebrospinal fluid; and finally, hydromeningocele, a hernia of only the meninges, which enclose cerebrospinal fluid. It is believed that all these forms originate from encephalocystocele and represent only separate stages in the development of cerebral hernias. Clinically, anterior hernias manifest as the presence of a tumor located around the circumference of the root of the nose, at the inner or outer corner of the eye. The tumor usually does not reach the size of an orange; the skin over it is either completely normal or thinned. The tumor is compressible to a certain extent. When straining, the tumor tightens and increases in volume. Anterior cerebral hernias occur 3 times more often than posterior ones; posterior ones sometimes reach enormous sizes and usually have a stalk. Cerebral hernias must be differentiated mainly from hemorrhages, blood tumors of newborns, dermoid cysts, and angiomas. Location in the region of the parietal tuberosities, non-reducibility, and the absence of a bony ridge argue in favor of a blood tumor. Dermoid cysts are located exclusively at the fontanelles, where cerebral hernias never occur. It can be difficult to distinguish anterior cerebral hernias from an angioma, however, location in the region of the sagittal suture, the occasional presence of vascular murmurs, and clearer pulsation help distinguish an angioma. The course of cerebral hernias is always unfavorable; sooner or later their bearers are doomed to death. Conservative methods of treatment are now abandoned as failing to achieve the goal, but radical intervention also does not yield good results: Petrov out of 146 operated cases counts up to 40% mortality. Anterior hernias are particularly unfavorable. The usual complication that destroys the operated patients is purulent meningitis. The surgical measure should be reduced, firstly, to the removal of the hernia contents and, secondly, to the closure of the defect. The first stage presents no difficulties, except for the presence of the brain in the hernia sac, when removal is impossible. Closure of the defect is performed either only with skin covers or with the help of a bone-periosteal flap on a stalk taken adjacently from the region of the superciliary arches, where the bone is quite thick, so that there is no danger of opening the craniocerebral cavity.

Injuries to the bones of the S. constitute an important chapter in clinical surgery, not only in themselves, but also due to the complications that so often accompany them. Usually, bruises of the bones of the S. are the result of external blunt trauma. The bruises themselves are not of great importance, but they are often accompanied by shock and intracranial hemorrhages. Usually, if only the soft tissues of the S. are bruised, there is a limited swelling in the area of the bruise, painful on pressure, or an accumulation of blood—a hematoma—which quickly resorbs under the influence of rest and cold. Bruises accompanied by concussion or hemorrhage proceed with cerebral phenomena: in the first case, with loss of consciousness that quickly passes without leaving consequences; in the second case, besides loss of consciousness, which can persist for a long time, they are accompanied by local focal phenomena: convulsions, pareses, paralyses, etc. Treatment in this case should consist of absolute rest, and if the phenomena intensify, of decompressive surgery. Bruises are often complicated by fractures of the bones. Wounds of the bones of the S. are encountered in practice quite often, especially during wartime. Wounds can be punctured, incised, or chopped. Anatomically, wounds are differentiated as linear or flap-like. One should also distinguish wounds that do not penetrate the cranial cavity (Figure 13. Lymphatic vessels and regional lymph. glands of the head: 1-lgl. occipitales; 2-lgl. auric, post.; 3-lgl. cervic. prof.; 4-truncus lymphaticus jugularis; 5-v. jugul. int.; 6--a. carotis comm.; 7-lgl. submaxill.; 8-lgl. auric, ant.) and wounds that do penetrate. The latter type of wound usually proceeds with complications. Bruised wounds are more common than incised wounds. They already have the character of a fracture with displacement of fragments, sometimes with their deep penetration into the cranial cavity. In wartime practice, gunshot wounds of the S. are most common; they can be divided into two main groups: those that do not penetrate the cranial cavity and those that do. The difference between them is very significant, because in the second case, complications immediately appear after the injury, sometimes absolutely fatal. These injuries deserve attention because usually up to 70% of such wounded die on the battlefield (Razumovsky). Non-penetrating injuries are treated like ordinary soft tissue injuries, taking into account the special conditions of the location of the galea aponeurotica, which in purulent processes predisposes to spread. The external appearance of gunshot injuries to the bones of the S. is very diverse. Several types of cranio-cerebral injuries are distinguished: injuries at close range, which due to hydrodynamic action break the S. and brain into pieces, and injuries at longer distances, in which two types of wounds are distinguished: a) so-called tangential wounds, more superficial, forming a groove in the S. and brain; b) so-called diametrical, piercing the S. and brain along one of the long diameters, resulting in either a through-and-through wound or a blind one. The wounded in the S. die in the initial period either from destruction of life-important centers or from concussion of the brain; in later periods—from inflammatory processes of the brain and its membranes. With tangential wounds, careful primary treatment is necessary with removal of fragments, foreign bodies, freshening of the bone, brain, and tissues, with tight closure, provided the wounded person arrives no later than 12 hours. In other cases—open method of treatment. For through-and-through wounds, there are two methods of treatment: conservative and surgical, with the advantage still being the latter, in which, if performed in the first 8-12 hours, bone fragments and foreign bodies are removed, preventing subsequent complications. Conservative treatment is indicated in cases of late arrival of the wounded without the presence of cerebral complications. With injuries to the S., the difference between the entrance and exit wounds is particularly pronounced: the entrance wound is round, of small size; the exit wound is of larger size, with damaged, cracked, crushed edges. The clinical picture of gunshot injuries to the bones of the S. is extremely diverse and highly varied in its manifestations. Sometimes all signs are expressed very weakly, and the wounded person instantly falls dead. Between these extremes, a whole range of intermediate degrees is observed. Fractures of the S. Fractures of the vault of the S. are more common than fractures of the base. According to Murney, this ratio is expressed as 77% and 23%, according to Dukhanin—as 87% and 13%. They can be the result of direct or indirect violence. In the first case, the fracture occurs at the site of the action of violence; with fractures from indirect violence, it is a matter of compression of the S., and its integrity is violated outside the points of application of force. Fractures are distinguished as complete and incomplete. In the first case, it is a fracture of the lamina vitrea, while the lamina externa remains undamaged, and in the second case, the fracture extends to both plates. Clinically, with incomplete fractures without cerebral phenomena, such a fracture can easily be mistaken for a bruise, and only an X-ray gives the true picture of the injury, which is why an X-ray should be taken for any bruise of the S. to prevent subsequent cerebral complications (epilepsy). From an anatomical point of view, fractures are divided into: a) linear, b) multiple, c) star-shaped, d) comminuted, e) depressed, and f) fractures with comminution. Complications that occur with fractures of the cranial vault manifest themselves primarily in intracranial hemorrhages and compressions. The clinical picture of fractures of the cranial vault is very diverse: sometimes it is expressed very weakly, and sometimes it ends in death on the spot. Local signs of the fracture consist in tenderness of a certain area of the cranial vault, in hemorrhage and bruises at the site of the fracture and in its nearest vicinity. On palpation, if the fracture is not complicated, one can feel a depression or protrusion of the fragment, and sometimes mobility of the fragment. With open fractures, the matter is simpler. General signs of fractures of the cranial vault come down to signs of severe injury: vomiting, rare tense pulse, convulsions, paralyses, incontinence of urine and feces, stertorous breathing, unequal dilation of the pupils, complete loss of consciousness. Treatment should consist, in case of incorrect position of fragments or signs of brain compression, in the surgical removal of fragments. With cracks without cerebral phenomena, treatment should be conservative—rest, cold to the head. The diagnosis is much more difficult to establish with fractures from indirect violence, when the application of force is in one place, and the fracture is on the other side; these are so-called contre-coup fractures. In these cases, there is a violation of the bone or rupture of a vessel, for example, the a. meningeae mediae, on the side opposite the blow. In this case, the phenomena from the brain side and X-ray examination should indicate the site of injury. With severe cerebral phenomena, surgical intervention is indicated according to focal phenomena. Fractures of the base of the S. in most cases represent a fairly typical clinical form. The line of fracture can go in longitudinal, transverse, diagonal, or ring-shaped directions. Displacement of fragments is usually insignificant. Clinically, a fracture of the base of the S. is characterized primarily by signs of severe injury and of a cerebral nature: the general severe condition of the victim, phenomena of bruise or compression of the brain, unconscious state, stertorous breathing, change in pulse. Bleeding from the nose, ear, and orbits is particularly important. Bleeding from the orbit is expressed in the appearance of subconjunctival ecchymoses. With fractures of the base of the S., the damage can affect only the bone, and in these cases we have the above-mentioned phenomena. Sometimes these fractures are complicated by rupture of the dura mater, as a result of which sometimes there is leakage of cerebrospinal fluid from the ear, nose, and even entry of air into the cranial cavity and ventricle due to pulsatory oscillations of the brain and suction of air into these cavities, which also often leads to infection and meningitis. Sometimes the rupture of the dura mater is valve-like, which sometimes closes, and sometimes with strong straining opens and leads to abundant discharge of fluid. The prognosis is extremely serious. Cases without complications are treated conservatively—rest, ice to the head. With complications by cerebral phenomena, some recommend surgical intervention, expressed in decompression. Spasokukotsky proposed for injuries to the S. to perform massive (500-600 cm³) bloodlettings, which give very rapid and reliable improvement in the general condition, disappearance of headache. Inflammatory diseases of the bones of the S. can be acute and chronic. Acute inflammatory processes here manifest as 1) acute periostitis, 2) acute osteomyelitis, and 3) acute inflammation of the veins of the cranial bones. The cause of acute periostitis is either trauma or direct spread of the process from the soft tissues or from the cranial cavity. Locally, there is a picture of either an abscess or a phlegmon. The swelling is usually of considerable size, but never crosses the boundary of attachment of the galea aponeurotica.

Prognosis is favorable.-Treatment is usual for acute purulent processes with counter-openings at the level of attachment of galea aponeurotica.-Acute osteomyelitis is either a direct transition of the inflammatory process from the periosteum or a manifestation of infectious osteomyelitis. Anatomically, it amounts to the necrosis of a certain area of bone with subsequent sequestration of the necrotized bone. A feature is that sometimes the process is not delimited and sequestration does not occur, therefore the course is prolonged; in these cases, treatment should be conservative, and operative only in cases of complete sequestration.-Inflammation of the veins of the cranial bones is a consequence of particularly severe purulent inflammation of the soft parts of the skull or as a complication of thrombosis with suppuration of the cerebral sinuses. Clinically, it proceeds with symptoms of general sepsis, with cerebral symptoms. Prognosis is poor. Among chronic inflammatory processes, tuberculosis occurs, which proceeds either in an infiltrative-progressive form with the formation of granulations, or as a sequestrating form with the formation of small sequestra, or as a perforating form when the entire thickness of the bone is destroyed. Clinically, tuberculosis of the cranial bones gives a particularly clear picture in cases where it leads to the formation of a cold abscess and subsequent fistulas.-Syphilis of the bones of the skull is quite common; according to some authors, gummatous lesions of the bones of the skull are observed in 19-20% of all bone manifestations of syphilis. All forms of bone lesions are encountered: osteitis, periostitis gummosa, sequestra, etc. A very characteristic feature is that in syphilis, along with destructive processes, the bone shows considerable regenerative abilities, as a result of which it acquires a very characteristic appearance: on the one hand, the bone appears eaten away, destroyed, and on the other hand, covered with bone outgrowths, tubercles, etc. Prognosis is generally favorable. Recognition of syphilis of the cranial bones is based on data characteristic of bone syphilis in general.-Actinomycosis of the cranial bones is rare. The clinical picture consists of signs of a chronically proceeding inflammatory lesion of the bones of the skull in the presence of a characteristic actinomycotic infiltrate in the soft tissues with its discharge. Treatment consists of operative and medicinal measures. Tumors of the bones of the skull are either primary, with their starting point being the bone itself, or secondary, with the tumor spreading to the bone from the coverings or from the contents of the skull. Among primary tumors, exostoses and osteomas are encountered; they grow slowly and do not cause particular subjective disorders; however, if they develop into the cranial cavity, they can cause cerebral symptoms. Cholesteatomas of the skull are more common in the temporal bone. A cholesteatoma is a tumor of pearly-white color, characteristic crumbly consistency, soft to the touch. Microscopically, masses of keratinized epidermis are found with an admixture of cholesterol crystals and fatty acids.-Special mention should be made of the cyst-like formations called sinus pericranii. By this name is meant a cystic formation containing venous blood. This formation lies between the bone and the periosteum and is connected with the contents of the skull. The etiology of this disease is unclear. Treatment is usually operative, but presents certain technical difficulties, as one has to deal with bleeding from the veins of the cranial bones. The most convenient method is to perform trepanation with ligation of the feeding vessels. However, cases have been described where bleeding was stopped by muscle tamponade. Among malignant tumors of the bones of the skull, cancer occurs, which is secondary. The lesion of the bones has a creeping character. Anatomically, it appears as a superficial ulcer with ragged edges and an uneven bottom. Sarcoma of the bones of the skull is either primary bone, actually originating from the bone, or secondary-as a result of the growth of a tumor from the cranial cavity or from the coverings. Round-cell and spindle-cell sarcomas, sarcomas of vascular and myxomatous structure are encountered. Sarcomas originating from the periosteum are of denser structure; sarcomas originating from the diploë are softer. Sarcomas developing from the bony part have the properties of osteosarcomas. Finally, myelogenous sarcomas occur; they have a capsule and are surrounded by proliferated periosteum. Clinically, it should be noted that sarcomas are of large size and have very little tendency to ulcerate. Treatment consists of operative intervention. Echinococci are rarely found in the bones of the skull. Cases of echinococcus of the temporal muscle, frontal muscle, frontal sinus, ethmoidal sinus have been observed. In all these cases, the matter leads to the erosion of the bone and the growth of the tumor into the cranial cavity. Treatment consists of removal of the CYST,