SURFACE FORM OF THE SKULL. 223 



zygomatic arches, touching the temporal ridges, they meet over the top of the head, instead of 

 being parallel, or nearly so, as in the European skull, in which the zygomatic arches are not 

 nearly so prominent, 'this gives to the face a more or less oval type. 5. Behind the ear is the 

 mastoid portion of the temporal bout-, plainly to be felt, and terminating below in a nipple- 

 shaped process. Its anterior border can be traced immediately behind the concha, and its apex 

 is on about a level with the lobule of the ear. It is rudimentary in infancy, but gradually 

 develops in childhood, and is more marked in the negro than in the European. 6. The external 

 occipital protuberance is always plainly to be felt just at the level where the skin of the neck 

 joins that of the head. At this point the skull is thick for the purposes of safety, while 

 radiating from it are numerous curved arches or buttresses of bone which give to this portion of 

 the skull further security. 7. Running outward on either side from the external occipital protu- 

 berance is an arched ridge of bone, which can be more or less plainly perceived. This is the 

 superior exrrnl \'u\? of the occipital bone, and gives attachment to some of the muscles which 

 keep the head erect on the spine ; accordingly, we find it more developed in the negro tribes, in 

 whom the jaws are much more massive, and therefore require stronger muscles to prevent their 

 extra weight carrying the head forward. Below this line the surface of bone at the back of the 

 head is obscured by the overlying muscles. Above it, the vault of the cranium is thinly covered 

 with soft structures, so that the form of this part of the head is almost exactly that of the upper 

 portion of the occipital, the parietal, and the frontal bones themselves; and in bald persons 

 even the lines of junction of the bones, especially the junction of the occipital and parietal at 

 the lambdoid suture, may be defined as a slight depression, caused by the thickening of the 

 borders of the bones in this situation. 8. In the line of the greatest transverse diameter of the 

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

 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. 

 0. 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 170) 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 tttpercQiary 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 

 iinatil boin'-s 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 



