396 PROFESSOR OWEN ON THE OSTEOLOGY OF 



and there is a distinct connecting ridge between the posterior outer and the anterior 

 inner cusps, as in the first molar (m 1), and which ridge is not developed in the last 

 molar of the TV. niger. 



In comparing the interior of the cranium the olfactory fossa is much deeper in the 

 Tr. Gorilla than in the Tr. niger, and the ' crista galli ' is either more rudimental than 

 in Tr. niger, or is absent, and there is no ridge continued upwards from the fossa upon 

 the inner surface of the frontal bone as in Tr. niger. The optic chiasma indents the 

 presphenoid with a deeper transverse groove in the Tr. Gorilla. The foramen lacerum 

 anterius is subquadrate in Tr. Gorilla : it is triangular in Tr. niger by the elongation of 

 the upper and outer angle. The roofs of the orbits form a more convex prominence in 

 the interior of the cranium on each side the olfactory fossa in Tr. niger than in Tr. Gorilla. 

 The posterior clinoid ridges overhang the sella turcica in the Tr. niger, in which they 

 are more produced forwards than in Tr. Gorilla. The fossEe for the middle lobes of the 

 cerebrum or ' natiform protuberances ' are deeper in the Tr. niger than in the Tr. Gorilla. 



The inner surface of the cranium of the Tr. Gorilla is smooth and even ; the indi- 

 cations of the convolutions of the brain are very feeble ; the middle meningeal artery 

 leaves impressions of its chief ramifications on the sides of the cavity ; the longitudinal 

 sinus begins to indent the inner surface of the calvarium near the end of the sagittal 

 suture, which however was obliterated in all the specimens ; it descends to the middle 

 of the supraoccipital surface, then divides into the lateral sinuses which form deep chan- 

 nels at the back part of the petrosal on the inner surface of the mastoid. 



The lateral walls of the cranium formed by the lower borders of the parietals are thin 

 and diaphanous, but compact and without diploe ; this is the case also with some parts 

 of the supraoccipital plate : but the cranial walls are remarkably unequal in thickness ; 

 there is much diploe along the base of the sagittal and lambdoidal crests, and this 

 receives air where it is continued upon the mastoids. 



Tlie sinuses of the basisphenoid were divided by a complete septum in one specimen, 

 but this was absent in another ; they extend into the alisphenoids and into the bases of 

 the pterygoids. The frontal sinuses are divided by a strong vertical septum, whence 

 they extend outwards to the base of the external orbitar process ; they also reach far 

 back and communicate, as in Man, with the middle meatus of the nose, above the 

 smaller opening of the antrum. 



The inflated or posterior part of the maxillary has thin, almost papyraceous walls : 

 the vast antrum extends to the floor and inner wall of the orbit and into the malar bone ; 

 it communicates with the nostrils by a wide aperture, overarched by the inferior turbinal, 

 and sometimes also by a smaller opening overarched by the turbinal process above. Its 

 walls being broken away on the left side in a skull of an old male Tr. Gorilla, shows what 

 appears to be the convex back part of a second wall of the antrum, about half an inch 

 from the outer one, and which is cribriform or reticulate : a portion of this convexity, 

 removed vertically on the right side of the same skull, exposed a light and delicate 



