Edmund Owen

“ The Orbit.—Each orbit is a pyramidal cavity, the base of the pyramid being in front, at the orbital margin, and the apex behind, at the optic foramen, where the optic nerve and ophthalmic artery pass through. The four sides of the pyramid form the roof, floor, inner and outer walls of the orbit. The roof is arched from side to side and is made up of the frontal bone anteriorly, and the lesser wing of the sphenoid posteriorly. The floor is chiefly formed by the maxilla, though the malar forms a little of it in front. ”

“ The thick covering of the brain, the dura mater, is thus exposed, and if the presence of a tumour (or an abscess) has caused an excess of intra-cranial pressure, the membrane will bulge into the opening. The dura mater is then incised and turned down, and if the tumour is upon the cortex of the brain, and not too extensive, it is taken away. It may be necessary, however, to enlarge the opening made in the skull, and to break through a considerable mass of brain-tissue before the tumour can be removed. ”

“ About two-thirds of the way back the sagittal suture becomes less serrated and on each side of it the small parietal foramen may be seen. This only transmits a small emissary vein (see Veins) in the adult, but, as will be seen later, is of considerable morphological interest. As middle life is reached the cranial sutures tend to become obliterated and the bones can no longer be separated; this fusion begins at the places, where the sutures are least deeply serrated, and as a rule the sagittal suture disappears between the two parietal foramina between thirty and forty years of age. ”

“ The Skull from in front (norma facialis) (see fig. 1) . The forehead region is formed by the frontal bone, the two halves of which usually unite in the second year; sometimes, however, they fail to do so and then a suture (metopic) may remain to an advanced age. The lower limit of the forehead is formed by the upper margin of the orbit on each side, and by the articulation between the frontal and nasal bones near the mid line. ”

“ On the upper (dorsal) surface of the skull are two apertures in the middle line"; the more anterior of these is sometimes called the anterior fontanelle, though it has nothing to do with the bregma, described in man's skull, but forms a rudimentary median orbit for the pineal eye (see Brain) . The posterior fontanelle is a depression which leads into two lateral tubes, each of which passes into the auditory capsule and is known as an aqueductus vestibuli (see Ear) . ”

“ In the side view of the face the nasal and maxillary bones are seen, and from this point of view it will be noticed that just below the nasal aperture the maxillae, where they join, are produced forward into a little spur, the anterior nasal spine, which is a purely human characteristic. At the side of the maxilla the malar or jugal (Ma) bone is placed, and its lozenge-shaped outline is apparent; it forms the anterior part of the zygomatic arch. When the mandible is disarticulated and removed the posterior part of the maxilla is seen, and behind it the external pterygoid plate of the sphenoid. ”

“ In the bony fishes (Teleostei) the membrane or dermal bones are still more numerous, and many of them are unrepresented in the mammalian skull, while others, which are there quite rudimentary, are very large. The chondro-cranium tends to disappear in the vault, but the base is fully ossified. Among other cartilage bones the five ossifications of the auditory capsule are seen, the pro-, epi-, opisth-, pter- and sphen-otics, all of which are found as centres of ossification in man. ”

“ Dividing the posterior nasal aperture into two is the vertical hind edge of the vomer (v) , which articulates above with the body of the sphenoid (basi-sphenoid) , and just behind this the sphenoid is united by bone with the basioccipital (b) , though up to twenty years of age there is a synchondrosis (see Joints) called the basilar suture) between them. It is therefore very easy to tell an adult's skull from that of a young person. ”

“ Inasmuch as many of the tumours are destitute of a limiting wall, a considerable mass of brain-tissue has to be traversed in order to remove the growth, and the ultimate result, so far as the impairment of functions is concerned, is a serious disappointment. If, however, the tumour is found to be encapsuled, its removal is sometimes quite easily effected, and perfect recovery is then likely to be the result. ”

“ On the lower surface of the petrous bone is the round opening of the carotid canal through which the internal carotid artery and its accompanying sympathetic nerves pass into the skull, while more externally the styloid process projects downward and forward and is more or less ensheathed at its root by the rampart-like ridge of the vaginal process. Between the styloid process and the occipital condyle lies the jugular or posterior lacerated foramen through which pass the lateral and inferior petrosal sinuses, and the glosso-pharyngeal, vagus and spinal accessory nerves. ”

“ In the Elasmobranchii (sharks and rays) and Holocephali (Chimaera) among the fishes the skull is still a complete cartilaginous box, though calcification of the cartilage often takes place. Taking the skull of the dogfish as a type, two large olfactory capsules are seen in front, and behind these the cranial brain-box is narrowed, being excavated at its sides for the great orbits. More posteriorly the auditory capsules widen the skull, and on the posterior (caudal) aspect the foramen magnum is seen with an occipital condyle on each side of it for the first vertebra to articulate with. ”

“ Fractures of the base of the skull are often associated with bleeding from the nose, mouth or ear, or with extravasation of blood over the eyeball. Facial paralysis is the result of the line of fracture passing across the bony channel in which the seventh or facial nerve is running. ”

“ At the root of this process is the glenoid cavity where the condyle of the lower jaw articulates, and just behind this the external auditory meatus is seen (em) . Behind this again the mastoid temporal is prolonged down into a nipple-shaped swelling, the mastoid process (MT) , containing air cells and only found in the adult human skull, while just in front of the external auditory meatus is the styloid process (St) , connected with the hyoid bone by the stylo-hyoid ligament (dotted) . ”

“ Many of the bones are pneumatic, the process reaching its maximum in the elephant and the adult male gorilla. The periotic. capsule blends with the squamosal and tympanic to form the petrous bone, though it is practically only in man that the second visceral arch ossifies on to this as a styloid process. There are usually two occipital condyles which have basi- and exoccipital elements, though there are many mammals in which there is one large crescentic condyle surrounding the anterior half of the foramen magnum. ”

“ The notochord (see Skeleton: Axial) extends forward to the ventral surface of the middle cerebral vesicle (see Brain) or as far as the place where the dorsum sellae will be. It is partly surrounded by the mesenchyme just as it is completely in the rest of the axial skeleton, and this mesenchyme extends dorsally on each side to wrap round the nerve cord, which is here the brain. ”

“ The heart being loaded with imperfectly aerated blood, the face is dusky or livid, and the pulse is slow and full. No notice is taken by the man of a loud shout into his ear, and on the surgeon raising his eyelids the pupils are found dilated and fixed, which signifies that the reflex to light is lost — a very grave sign. ”

“ The single occipital condyle, if looked at in a young specimen, is seen to consist of a basioccipital and two exoccipital elements, though these are indistinguishable in the adult. The parasphenoid is represented by a broad plate which is called the basitemporal. The pro-, epi- and opisth-otic bones fuse together to form the auditory capsule.
In the Mammalia the calvaria varies considerably in the different orders, the characteristic features being best marked in adult males. ”

“ As a rule, the pupils react to light, contracting as the lids are raised. This shows that the light-reflex is not lost, and is a good omen. One of the first signs of returning consciousness is that the person vomits, and after this he gradually comes round. ”

“ Inasmuch as the reflex actions are in abeyance, it will be necessary to have the bladder regularly emptied. The man should be placed on his side in bed, so that his tongue may not fall back and choke him, and if it is thought inadvisable to bleed him, a full dose of calomel should be administered. ”

“ The person may die from the concussion, or he may slowly or quickly recover. The insensibility may be for a time complete . The pulse may be small, quick and imperceptible, and, no blood being pumped up by the enfeebled heart, the face will be pale and the surface of the body cold. ”

“ It has more recently been shown by Levi that the same thing is true for man. K. Gegenbauer has pointed out that the primitive membranous skull shows, in the chordal region, signs of metameric segmentation in the way in which the cranial nerves pierce the dura mater one 'behind the other. These segments, however, had lost their distinctness even before the cartilaginous cranium had become developed, so that there is no real segmental value in the elements of this, still less in those of the bony skull. ”

“ Ossification of the processes of the dura mater occurs in the tentorium cerebelli of the carnivora and in the falx cerebri of the ornithorhynchus and porpoise. The orbits are in most mammals continuous with the temporal fossae. Sometimes, as in many of the ungulates and in the lemurs, they are outlined by a bony ring, but it is not until the higher Primates are reached that the two cavities are shut off and even then a vestige of their original con- tinuity remains in the spheno-maxillary fissure. ”