214 THE CRANIA OF THE SIMIIDAE (PRIMATES) [SECT. A 



from the former (the Cercopithecidae) the following points may be mentioned. 

 Thus in the Hylobates the brain-case is proportionately larger in comparison 

 with the facial skeleton, the contour is ovoid, the surface of the cranium is 

 devoid of prominent crests, though the outline of the area occupied by the 

 temporal muscle is shewn by an upraised linear ridge. The cranial capacity 

 varies from 76 c.c. to 90 c.c. in this species and the sexual difference is very 

 small (Oppenheim). The sutures demand no special mention. The orbital 

 cavities are remarkably capacious. The latter feature is associated with the 

 small size of the animal, in accordance with a general law as to the proportions 

 subsisting between the animal's absolute bulk and the size of the eyes. This 

 feature modifies the appearance of post-orbital lateral compression (of the 

 skull), which is really present. 



Turning now to other facial characters, it will be seen that the orbital 

 margins are distinct or trenchant, that the lachrymal hamulus is vestigial, that 

 the os planum of the ethmoid is not infrequently divided into anterior and 

 posterior portions, and that the spheno-maxillary fissure is widely open. The 

 infra-orbital suture does not persist on the facial aspect. The nasal aperture 

 has an ovoid form or contour, with margins which are obliterated inferiorly. 

 No nasal spine is seen : the nasal bones are early conjoined by synostosis, 

 and the compound bone has a somewhat quadrate contour and is fiat, not 

 suggesting the prominence of the soft parts of the nose. The palate is 

 hypsiloid (U-shaped) in contour, with a diminutive posterior spine : the tuber 

 maxillare is also diminutive. In the region of the temporal fossa the rudi- 

 mentary character of the alisphenoid (as compared with its condition in Man) 

 is at once seen : this bone joins the parietal at the pterion : and the infra- 

 temporal crest is insignificant. 



At the base of the skull the shallowness of the glenoid fossa arrests 

 attention. Yet this shallowness cannot be taken to indicate much freedom of 

 the mandible in lateral movements. For the large canine teeth limit such 

 movements very considerably and markedly. No endoglenoid tubercle is 

 developed as in the Gorilla, though a post-glenoid process is distinct. Styloid 

 and vaginal processes are not seen. 



The dentition provides the normal formula for Catarrhine Primates. The 

 canines greatly exceed the neighbouring teeth in size : the molars are tetra- 

 cuspid and the talon in the lower molars is not conspicuous. 



The mandible is characterized by the shortness of the ascending ramus, 

 by the projection of the angle and by the absence of genial tubercles. The 

 vertical height of the body of the jaw in the region of the second molar tooth 

 is much less than the height at the first premolar tooth. Near the latter, the 

 jaw is deep and massive, and the same remark applies to the region in which 

 are implanted the incisor and canine teeth. Such an increase in strength is 

 related to the large size of the canine teeth, and it reproduces the condition 

 exhibited in an even more pronounced degree by the extinct cat named 

 Pogonodon (Cope). 



