66 THE OSTEOLOGY AND MYOLOGY 



early coalescence of the frontals, this portion of the crest is usually found single. From 

 the point of subsidence of the crest into the common coronal surface, two ridges diverge 

 at an acute angle and run forward and outward along the frontal to the superciliary pro- 

 tuberances, marking the extent of attachment of the temporals to the frontal. The 

 sagittal comb is thus forked, as it were, anteriorly. 



The roof of the nasal cavities appropriates most of the superior surface of the skull ; 

 occupying all the surface anterior to the supraorbital ridges, and the forks of the parietal 

 crest. This surface is everywhere smooth ; the most marked irregularity of contour is a 

 slight concavity on either side in the superior maxillaries, where the lower canine abuts. It 

 is divided longitudinally for three-fourths of its extent from before backwards by the nasal 

 suture — the neural spines never coalescing ; there is no inter-frontal suture in adult skulls ; 

 the other sutures are the irregularly curved and arched naso-maxillary, the fronto-nasal, the 

 naso-premaxillary, maxillo-premaxillary, and fronto-maxillo-lachrymal. A great part of the 

 OS lachrymale extends upon the superficies of the face ; the opening of its duct lies outside 

 the orbit. The only other opening upon the face is the foramen maxillare — situated just 

 above the interspace between the second and third premolars, and of great size. The 

 nasal aperture, of large size, is partially roofed over by the pointed projection of the two 

 nasal bones, and completed at the sides and in front by the produced premaxillaries. 



Vast temporal fosste result from the constriction of the brain-case, the great outward 

 sweep of the zygomata, and the imperfection of the bony orbits. The zygomatic process 

 of the squamosal may be traced backward to its origin in the mastoid portion of the crista 

 occipitalis as a prominent bony ridge, overarching the tympanic cavity. As soon as it fairly 

 leaves the squamous part of the bone, it sends downward the strong process that forms the 

 back wall of the glenoid, while at the same time its superior margin begins to rise. The 

 superior margin of the zygoma is thin and sharp ; its upward convexity is due as much to 

 the expansion of the bone itself, as to the concavity of the opposite margin. The latter — 

 the under border — is thickened, and has a well marked, oblique bevelling ; its concavity is 

 greatest anteriorly, where the malar bends downward to join the large out-standing zygo- 

 matic process of the maxillary. Posteriorly, the lateral view of the zygoma shows, at the 

 termination of the malar, a deep excavation — the profile of the glenoid. The side of the 

 zygoma is traversed by the oblique squamo-malar suture, which is never obliterated. Ante- 

 riorly, the superior margin of the zygoma is suddenly thickened, and becomes moderately 

 concave — this portion defining the extent of the orbit. The structure and relations of the 

 zygomatic arches are clearly displayed in the accompanying figures (9 and 10); these are 

 such as would lead us to infer the nature of the animal's food, were we dealing with a 

 placental mammal ; but in the present order their indications are not so reliable. 



The very imperfect orbits appear as pai'ts of the temporal fossiB, having no bony wall pos- 

 teriorly, and being only partially floored by the maxillaries. The contour is indicated exter- 

 nally by the above-mentioned concavity of the malar, anteriorly by the stout lachrymal, 

 internally by a very slight superciliary ridge and more decided supraorbital protuberances. 

 The lachrymal, frontal, and palatine make up the inner walls ; in the formation of which the 

 last named takes greatest part. This smooth, orbito-nasal septum is distinguished from the 

 directly continuous temporal fossa by a slight ridge extending obliquely downward and 

 backward from the supraorbital prominence to the orbitosphenoid, forbidding encroachment 

 of the temporalis upon the orbit itself The outer wall of the orbit seems to be formed 



