394 PROFESSOR OWEN ON THE OSTEOLOGY OF 



niger, which gives it an ovate form with tlie great end downwards, and thus it more 

 resembles the form of that aperture in Man. 



The orbits have a more subquadrate form, with the angles rounded off, in Tr. Gorilla 

 than in TV. niger ; but their periphery is less sharply defined, especially below, than in 

 Tr. niger. The eethmoidal cells are more swollen out, giving the interorbital space a 

 greater breadth below and the lachrymal fossae a more anterior aspect in Tr. Gorilla. 



The infraorbital canal is open from its posterior commencement to where it perforates 

 the lower border of the orbit, and it issues upon the face relatively lower and further 

 from the orbit in the Tr. Gorilla (21')- In two skulls of the Tr. niger the infraorbital canal 

 is overarched by bone at both ends, and is a deeper and narrower fissure at the inter- 

 vening part than in Tr. Gorilla : in a third skull of Tr. niger the canal is deeper, nar- 

 rower and longer than in Tr. Gorilla. 



The whole nasal bone is relatively longer, and the distance from the orbits to the 

 external nostril greater in the Tr. Gorilla. 



The malar bone is more convex outwardly, and is more remarkable for its vertical 

 extent : it is flatter and developed more transversely in the Tr. niger. 



The larger proportional size of the canines in Tr. Gorilla impresses a corresponding 

 difference upon the alveolar part of the maxillary bone in that species. 



In comparing the skulls of the two species by a view of their base (Plates LX. and 

 LXIII.),the first remarkable difference is the broad, flat, or slightly concave supraoccipital 

 surface of the larger species as compared with the uniformly convex character of the same 

 part in the other, the outline of this part being rounded in Tr. Gorilla and almost angular 

 in Tr. niger* : the difference is due to the much thicker and broader lambdoidal ridge in 

 the larger species, which prolongs the surface far beyond the cerebellar fossa, and gives 

 the condyles and foramen magnum a rather more advanced position as compared with the 

 TV. niger. The next character, which is also a more anthropoid one, though explicable 

 in relation to the greater weight of the skull to be poised upon the atlas, is the greater 

 prominence of the mastoid processes in the Tr. Gorilla (m, PI. LXIIL), which are repre- 

 sented by only a rough ridge in the Tr. niger {m, PI. LX.). These protuberances are 

 cellular, and with a very thin outer layer of bone in the Tr. Gorilla. The lower surface 

 of the long tympanic or auditory process (as, PI. LX.) is smooth and flat, or slightly 

 concave, in Tr. niger, and developes a slight tubercle anterior to the stylohyal pit (.-ss) : 

 in the TV. Gorilla the same process (28, PI. LXIIL) is more or less convex below, and 

 developes a ridge (i;), answering to the vaginal process, on the outer side of the carotid 

 canal (c) ; and in one instance the ridge extended, like the vaginal process in Man, the 

 whole length of the auditory process, the under surface of which was, as it were, 

 pinched up orcompressed from before backwards. 



* In one of the skulls of the male Tr. niger before me, there is a small vascular, supraoccipital foramen, like 

 that in certain jiaiTOts and pigeons, and which 1 have pointed out in the Dodo (Zool. Trans, vol. iii. p. 351). 



