SURFACE FORM OF THE SKULL. 119 



head, on each side of the middle line, are generally to be found the parietal eminences, one on 

 each side of the middle line, though sometimes these eminences are not situated at the point of 

 the greatest transverse diameter, which is at some other prominent part of the parietal 

 region. They denote the point where ossification of the parietal bone began. They are 

 much more prominent and well-marked in early life, in consequence of the sharper curve 

 of the bone at this period, so that it describes the segment of a smaller circle. Later 

 in life, as the bone grows, the curve spreads out and forms the segment of a larger circle, 

 si i that the eminence becomes less distinguishable. In consequence of this sharp curve 

 of the bone in early life, the whole of the vault of the skull has a squarer shape than 

 it has in later life, and this appearance may persist in some rickety skulls. The eminence 

 is more apparent in the negro's skull than in that of the European. This is due to greater flak 

 tening 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 from 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, pass- 

 ing backward in a curved direction, over the parietal bone, and, though less marked, still gen- 

 erally 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. Mr. Victor Horsley has recently shown, in an article on the "Topography of 

 the Cerebral Cortex." that the second temporal ridge (see page 62) can be made out on the 

 living body. 10. The frontal eminences vary a good deal in different individuals, being con- 

 siderably 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 increased 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 brain 

 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 forehead 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 

 iiusiil /Mines form the prominence of the nose. They vary much in size and shape, and to them 

 is due the varieties in the contour of this organ and much of the character of the face. Thus, 

 in the Mongolian or Ethiopian they are flat, broad and thick at their base, giving to these tribes 

 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 car- 

 tilages 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 superior maxillary bone and the malar bone, is plainly to be felt 

 throughout its entire length. It is continuous internally with the nasal process of the superior 

 maxillary bone, 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 lachrymal sac, which is situated above and behind it. 14. The 

 outline of the lower jaiv is to 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 pos- 

 terior border of the ramus can be felt extending down to the angle. A line drawn from the con- 

 dyle 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 is plainly to be 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. 



Surgical Anatomy. An arrest in the ossifying process may give rise to deficiencies or 

 gaps ; or to fissures, which are of importance in a medico-legal point of view, as they are liable 

 to De mistaken for fractures. The fissures generally 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 cerebro-spinal fluid, it is called a meningoce le : when the protrusion consists of brain 



