160 THE SKULL. [CHAP. 



and the olfactory fossae, completely overlying them both ; 

 and consequently the occipital region of the skull with the 

 foramen magnum behind, and the cribriform plate of the 

 ethmoid in front, are in the same general horizontal line 

 with the basicranial axis as in Man, and not perpendicular 

 to them as in the Dog. 



It is remarkable that the deviations from this general rule, 

 especially as regards the plane of the occipital surface, are 

 not in relation to the general position of the animals in a 

 descending series, from Man to the lowest Monkeys ; for the 

 occipital surface is nearly vertical in the anthropoid Gibbons 

 (Hylobatcs), especially // syndactylus (the Siamang), and 

 completely so in the American Howling Monkeys (Mycetes), 

 where the cerebral fossa does not project in the least degree 

 behind the cerebellar fossa; while in the Baboons (Cyno- 

 cephalus], among the Old World Monkeys, and still more 

 in some of the smaller forms of American Monkeys 

 (as Saimiris], the posterior development of the cerebral 

 fossa is so great as to throw the supraoccipital bone con- 

 siderably more into the posteriorly prolonged base of the 

 skull even than in man. 



The olfactory fossa is always small. It is not only very 

 short, but, in consequence of the considerable projection 

 inwards of the portion of the frontal forming the roof of the 

 orbit on each side of it, is both narrow from side to side, 

 and deep from above downwards. 



In most of the Siwiina, including the Gorilla and Chim- 

 panzee, the frontals meet along the middle line over the 

 presphenoid, between the mesethmoid in front and thr 

 orbitosphenoids behind ; but the Orang agrees with Man in 

 wanting this postethmoid union of the frontals, and so also 

 do some of the Cebidce. 



The fossa on the inner surface of the periotic for the 



