118 THE SKELETON. 



Surface Form. The various bony prominences or landmarks which are to be easily felt and 

 recognized in the head and face, and which afford the means of mapping out the important 

 structures comprised in this region, are as follows : 



1. Supraorbital arch. 8. Parietal eminences. 



2. Internal angular process. 9. Temporal ridge. 



3. External angular process. 10. Frontal eminences. 



4. Zygomatic arch. H- Superciliary ridges. 

 .5. Mastoid process. 12. Nasal bones. 



6. External occipital protuberance. 13. Lower margin ot orbit. 



7. Superior curved line of occipital bone. 14. Lower jaw. 



1. The supraorbital arches are to be felt throughout their entire extent, covered by the eye- 

 brows. They form the upper boundary of the circumference or base of the orbit, and separate 

 the face from the forehead. They are strong and arched, and terminate internally on each side 

 of the root of the nose in the internal angular process, which articulates with the lachrymal 

 bone. Externally they terminate in the external angular process, which articulates with the 

 malar bone. This arched ridge is sharper and more defined in its outer than in its inner half, 

 and forms an overhanging process which protects and shields the lachrymal gland. It thus pro- 

 tects the eye in its most exposed situation and in the direction from which blows are most likely 

 to descend. The supraorbital arch varies in prominence in different individuals. It is more 

 marked in the male than in the female, and in some races of mankind than others. In the less 

 civilized races, as the forehead recedes backward, the supraorbital arch becomes more prominent, 

 and approaches more to the characters of the monkey tribe, in which the supraorbital arches are 

 very largely developed, and acquire additional prominence from the oblique direction of the 

 frontal bone. 2. The internal angular process is scarcely to be felt. Its position is indicated 

 by the angle formed by the supraorbital arch with the nasal process of the superior maxillary 

 bone and the lachrymal bone at the inner side of the orbit. Between the internal angular pro- 

 cesses of the two sides is a broad surface which assists in forming the root of the nose, and 

 immediately above this a broad, smooth, somewhat triangular surface, the glabella, situated 

 between the superciliary ridges. 3. The external angular process is much more strongly marked 

 than the internal, and is plainly to be felt. It is formed by the junction or confluence of the supra- 

 orbital and temporal ridges, and, articulating with the malar bone, it serves to a very consider- 

 able extent to support the bones of the face. In carnivorous animals the external angular pro- 

 cess does not articulate with the malar, and therefore this lateral support to the bones of the face 

 is not present. 4. The zygomatic arch is plainly to be felt throughout its entire length, being 

 situated almost immediately under the skin. It is formed by the malar bone and the zygomatic 

 process of the temporal bone. At its anterior extremity, where it is formed by the malar bone, 

 it is broad and forms the prominence of the cheek ; the posterior part is narrower, and termi- 

 nates just in front and a little above the tragus of the external ear. The lower border is 

 more plainly to be felt than the upper, in consequence of the dense temporal fascia being 

 attached to the latter, which somewhat obscures its outline. Its shape differs very much in indi- 

 viduals and in different races of mankind. In the most degraded type of skull 1 as, for instance, 

 in the skull of the negro of the Guinea Coast the malar bones project forward and not outward, 

 and the zygoma at its posterior extremity extends farther outward before it is twisted on itself to 

 be prolonged forward. This makes the zygomatic arch stand out in bold relief,- and affords 

 greater space for the Temporal muscle. In skulls which have a more pyramidal shape, as in the 

 Esquimaux or Greenlander, the malar bones do not project forward and downward under the 

 eyes, as in the preceding form, but take a direction outward, forming with the zygoma a large, 

 rounded sweep or segment of a circle. Thus it happens that if two lines are drawn from the 

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

 being parallel, or nearly so, as in the European skull, in which the zygomatic arches arc 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 bone, 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 curved line of the occipital bone, and gives attachment to some of the muscles which 

 vf P i. 6rect n tlie spine ' a ? cor dingly< 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 

 fu en i t T 1 lm f s 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 ot the bones in this situation. 8. In the line of the greatest transverse diameter of the 



