402 PROFESSOR OWEN ON THE OSTEOLOGY OF 



developed : the oblique ridge joining the antero-internai to the postero- external cusp is 

 wanting. The sigmoid course of the prominent part of the enamelled surface resulting 

 from this ridge is a material mark of the closer affinity of the Chimpanzee to Man. 

 The whole grinding surface of the crown is more minutely wrinkled in the Orang. The 

 number of roots of both premolars and molars is the same in both Apes. 



The skulls of the great Chimpanzee and Orang offer very striking differences from 

 one another when viewed from above, looking down upon the vertex. The cerebral 

 dome is more prominent, and the chamber of the brain seems at first sight to be more 

 capacious in the Orang ; but it is not so absolutely, being only less masked by the 

 lambdoidal and supraorbital ridges than in the Chimpanzee, in which their extraordinary 

 development, with that of the base of the zygomata, changes the convexity of the outer 

 surface of the cranial dome into a concavity at its periphery : the anterior and posterior 

 parts of the calvarium are rendered broader in the Chimpanzee, the external orbital 

 processes are much stronger, and the whole cranium is both longer and larger in pro- 

 portion to the face. The supraorbital prominence renders the plane of the orbits more 

 vertical in the Chimpanzee, and a less proportion of these cavities is visible in the top 

 view than in the Orang. 



The means of comparing the lower jaw and teeth of the Troglodytes Gorilla of Africa 

 and the Pithecus fVurmbii of Borneo have not yet reached me. 



In the foregoing comparison the points in which the Troglodytes Gorilla offers a closer 

 resemblance to Man than the Pithecus Wurmbii does, are the following : — 



1 . The cranial part of the skull is larger in proportion to the facial part. 



2. The foramen magnum is more advanced, and its plane bends upwards two degrees 

 less from that of the basioccipital than it does in the Orang. 



3. The plane of the supraoccipital* forms an angle of 120° with that of the basiocci- 

 pital : in the Orang it forms an angle of 140°. 



4. The mastoid processes are convex cellular protuberances ; but in the Orang they 

 are rough ridges. 



.5. The precondyloid foramen is single on each side, and opens closer to the jugular 

 foramen. 



6. The presence of a vaginal process. 



7. The presence of a styliform process of the sphenoid. 



8. The shorter basioccipital and basisphenoid. 



9. The deeper glenoid cavities for the lower jaw. 



10. The wider posterior nares. 



11. The shorter and straighter zygomatic arches. 



12. The foramen ovale is completely perforated in the alisphenoid, but in the Orang 

 it is a notch, completed behind by the petrosal, and is of a longer and narrower form. 



* A line drawn from the back part of the foramen magnum to the spinous process at the middle of the lam- 

 bdoidal ridge crossing the line drawn along the basioccipital. 



