THE SKULL AS A WHOLE 149 



ance may persist in those suffering from rhachitis. The eminence is more apparent in the negro's 

 skull than in that of the European. This is due to greater flattening of the temporal fossa in the 

 former skull to accommodate the larger Temporal muscle which exists in these races. The 

 parietal eminence is particularly exposed to injury ^rom blows or falls on the head, but fracture 

 is to a certain extent prevented by the shape of the bone, which forms an arch, so that the force 

 of the blow is diffused over the bone in every direction. (9) At the side of the head may be felt 

 the temporal ridge. Commencing at the external angular process, it may be felt as a curved 

 ridge, passing upward and then curving backward, on the frontal bone, separating the forehead 

 from the temporal fossa. It may then be traced passing backward in a curved direction, over 

 the parietal bone, and, though less marked, still generally to be recognized. Finally, the ridge 

 curves downward, and terminates in the posterior root of the zygoma, which separates the 

 squamous from the subcutaneous mastoid portion of the temporal bone. (10) The frontal 

 eminences vary a good deal in different individuals, being considerably more prominent in some 

 than in others, and they are often not symmetrical on the two sides of the body, the one being 

 much more pronounced than the other. This is often especially noticeable in the skull of the 

 young child or infant, and becomes less marked as age advances. The prominence of the 

 frontal eminences depends more 'upon the general shape of the whole bone than upon the size 

 of the protuberances themselves. As the skull is more highly developed in consequence of in- 

 creased intellectual capacity, so the frontal bone becomes more upright and the frontal eminences 

 stand out in bolder relief. Thus they may be considered as affording, to a certain extent, an 

 indication of the development of the hemispheres of the cerebrum beneath, and of the mental 

 powers of the individual. They are not so much exposed to injury as the parietal eminences. 

 In falls forward the upper extremities are involuntarily thrown out, and break the force of the 

 fall, and thus shield the frontal bone from injury. (11) Below the frontal eminences on the fore- 

 head are the superciliary ridges, which denote the position of the frontal sinuses, and vary 

 according to the size of the sinuses in different individuals, being, as a rule, small in the female, 

 absent in children, and sometimes unusually prominent in the male, when the frontal sinuses are 

 largely developed. They commence on either side of the glabella, and at first present a rounded 

 form, which gradually fades away at their outer ends. (12) The nasal bones form the promi- 

 nence of the nose. They vary much in size and shape, and to them are due the variations in 

 contour of this organ and much of the character of the face. Thus, in the Mongolian or Ethio- 

 pian they are flat, broad, and thick at their base, giving to these races the flattened nose by which 

 they are characterized, and differing very decidedly from the Caucasian, in whom the nose, owing 

 to the shape of the nasal bones, is narrow, elevated at the bridge, and elongated downward. 

 Below, the nasal bones are thin and connected with the cartilages of the nose, and the angle or 

 arch formed by their union serves to throw out the bridge of the nose, and is much more marked 

 in some individuals than others. (13) The lower margin of the orbit, formed by the maxilla 

 and the malar bone, is plainly to be felt throughout its entire length. It is continuous inter- 

 nally with the nasal process of the maxilla, which forms the inner boundary of the orbit. At the 

 point of junction of the lower margin of the orbit with the nasal process is to be felt a little tubercle 

 of bone, which can be plainly perceived by running the finger along the bone in this situation. 

 This tubercle serves as a guide to the position of the lacrimal sac, which is situated above and 

 behind it. (14) The outline of the mandible may be felt throughout its entire length. Just in 

 front of the tragus of the external ear, and below the zygomatic arch, the condyle can be made 

 out. When the mouth is opened this prominence of bone can be perceived advancing out of the 

 glenoid fossa on to the eminentia articularis, and receding again when the mouth is closed. 

 From the condyle the posterior border of the ramus can be felt extending down to the angle. 

 A line drawn from the condyle to the angle would indicate the exact position of this border. From 

 the angle to the symphysis of the chin the lower, rounded border of the body of the bone may be 

 plainly felt. At the point of junction of the two halves of the bone is a well-marked triangular 

 eminence, the mental process, which forms the prominence of the chin. 



Applied Anatomy. The thickness of the skull varies greatly in different regions of the same 

 skull and in different individuals. The average thickness of the skullcap is about one-fifth 

 of an inch (5 mm.). The thickest portions are the occipital protuberance, the inferior portion of 

 the frontal bone, and the mastoid process. The thinnest portions are the occipital fossae, the 

 squamous portion of the temporal bone, and over certain sinuses and arteries. An arrest in the 

 ossifying process may give rise to deficiencies or gaps, or to fissures, which are of importance in 

 a medicolegal point of view, as they are liable to be mistaken for fractures. The fissures gener- 

 ally extend from the margin toward the centre of the bone, but gaps may be found in the middle 

 as well as at the edges. In course of time they may become covered with a thin lamina of bone. 



Occasionally a protrusion of the brain or its membranes may take place through one of these 

 gaps in an imperfectly developed skull. When the protrusion consists of membranes only, and 

 is filled with cerebrospinal fluid, it is called a meningocele; when the protrusion consists of 

 brain as well as membranes, it is termed an encephalocele ; and when the protruded brain is a 

 prolongation from one of the ventricles, and is distended by a collection of fluid from an accu- 

 mulation in the ventricle, it is termed a hydrencephalocele. This latter condition is some- 



