The different varieties of mankind present certain •ell-marked and characteristic peculiarities in the form of the skull. There are three typical forms of the skull which seem to be well established from the examination and comparison of a large number of crania—viz., the prognathous, the pyramidal, and the oval or elliptical cranium. When the upper jaw slopes forward, the insertion of the teeth; instead of being perpendicular, is oblique. A skull with this peculiarity is prognathous or prognathic (Gr. pro, forward, and gnathos, a jaw); the opposite condition being termed orthognathous or artiaospiatItie (Gr. orthos, upright). The negro of the Guinea coast and the negrito of Australia present the prognathous character in its most marked The pyramidal form is character ized by the breadth and flatness of the face, which, with the narrowness of the forehead, gives this shape to the head. The Mongolian and Esquimaux skulls belong to this type. The oval or elliptical type is that which is presented by the natives of western or south ern Europe. and which is not distinguished by any particular feature so much as by the absence of the longitudinal projection of the first type, or the lateral projection of the second, and by a general symmetry of the whole configuration. The length of the skull, which to a great degree corresponds to the degree of development of the posterior cerebral lobes, has been taken by the late prof: Eetzius as a basis of elessification. He arranges all the varieties of mankind into two great classes—the doliencephahr, or long heads, whose cerebral lobes completely cover the cerebellum; and the brachycephalie, or short-heads, in whom the cerebral lobes do not extend so far. Each of these classes con tains orthognathous and prognathous varieties. See ETHNOLOGY.
It has been already stated in the article SRE LETON that the skull is only the anterior prolongation of the backbone, and that it consists of four yertebric or segments, corres ponding to the four consecutive enlargements of the nervous system which ultimately form the brain—viz., the rhinencephalon, the prosenceplailon, the mesencey &don, and the epencepludon —embryonic segments giving rise to the nerves of smell, sight, taste, and hearing. These four vertebrae, taken from behind forward, are termed the occipital, the parietal, the frontal, and the nasal vertebrae. For the anatomical evidence by which these crania] vertebrae are cesolved into the essential elements of a vertebra, as described in the article SKELETON, we must refer to prof. Owen's various works on the skeleton, or to the admirable summaries of them contained in Ilumpliry On the Human Skeleton (for which we are indebted to many of the details introduced into this article), aid to Holden's human Ostology. There has been much discussion as to who originated "The Theory of the Vertebrate Skull." The claim undoubtedly rests between Goethe, the great poet, and Oken, one of the most original and distinguished comparative anat omists of the early part of the present century. We believe the truth to be that the idea of the true nature of the skull flashed across the poet's mind in 1790, but that nothing definite was published on the subject till 1807, when Oken independently arrived at and promulgated similar views. Our limited space has prevented its from noticing the skull of birds, reptiles, or fishes. On these subjects the reader is referred to Huxley's Lectures on Comparative Anatomy, 1864, in which the structure and development of ibe human skull, as well as the skulls of all the lower vertebrate animals, are most copiously and philosophically discussed.
Fracture of the skull is an accident of such importance as to demand a special para graph. As already remarked, fracture may take place either in the vault or the base of the skull. We shall first consider/me/uses of the vault. Here the fracture is usually direct, the bone giving way at the point at which it was struck, and the result being either a simple fissure or a breaking of the bone into several fragments (a comminuted fracture). Although fractures may be limited to the outer or to the inner surface of
the skull, they most commonly extend through the whole ,thickness, and the broken bone is generally driven inward; and the most ordinary form of fracture with depres sion is that in which several fragments of a somewhat triangular form have their points driven down and wedged into each other, while their bases remain on a level with the surrounding hone. There ire no signs by which we d n in all cases recognize the exist ence of fracture of the vault. " Fissures," says Mr. Prescott Hewett, " involving the whole thickness of the vault of the skull, constantly exist without ever having been suspected during life, and even an extensive and comminuted fracture, with great depression of the fragments, may, and often does, creape notice when the broken bone lies hidden under the temporal muscle or under a large extravasat ion of blood."—Holmes's System of Surgery, vol. ii p. 116. When. however, the fracture is accompanied by a wound leading down to the bone it may, in general, be easily de tested. With regard to treatment, it is now an established rule that simple fractures of the skull with depres sion, and without symptoms, are to be let alone. The depression may be so marked as to be easily detected; and yet so loug as there are no symptoms all operative interfer ence,.of whatsoever form, is carefully to be ,avoided."—Prescott Hewett, op. cit. If, however, there be a wound leading down to the bone in a•depressed fracture without symptoms, immediate operative interference is called for. When a depressed fracture is accompanied by primary 1w:tin-symptoms, an operation for the purpose of raising or removing the depressed fragments is usually necessary. If, however, the fracture is a simple one, and the symptoms are not urgent, milder remedial agents, as bleeding,. purg lug. and low diet may be first tried. Cases occasionally occur in which very urgent symptoms of cerebral pressure persist for a long time, and are relieved at once ou the pressure being removed. A remarkable case is recorded by Cline (Medice(lhir. Rey., vol. i. p. 471), in which a sailor remained in a state of unconsciousness for 13 months in cousequenee of a wound causing fracture and depression of one of the parietal bones. Cline trepanned the part and elevated the bone, and on the evening of the same day, the sailor sat up in bed, and though at first stupid and incoherent, soon became rational and well, upward of a year having elapsed in which his life was a complete blank.
Fractures of ihe base may be direct or indirect, but in most cases are indirect, that is ' to say, the bones give way at a point remote from the seat of the blow, as has been already shown. At certain parts, however, the bones of the base are so thin that if direct pressure be brought to bear upon them they readily give way. Thus scissors, slate-pencils, tobacco-pipes, etc., have often been thrust into the skull through the orbits the nostrils, and these wounds are very serious, from the readiness with which the brain may be thus injured. The only symptoms that can be depended upon as indicat ing a fracture of the base of the skull are connected either with an escape of the sub stance of the brain, or blood, or watery fluid, or with an injury done.to the nerves as they Emerge at the base. Out of 33 cases of fractured base observed by Hewett, bleed ing from the mouth or nose occurred in 14 and bleeding from the ear in 15 cases. A. copious watery discharge from the ear was, until very recently, regarded as a diagnostic sign of fracture of the base; and there can be no doubt that when such a discharge of cerebrospinal fluid occurs either from the ear or nostrils, that it most probably is con nected with fracture. Operative interference is very seldom required la these frac tures, our treatment being directed not against the broken bones, but against the accompanying cerebral lesions.