General Osteology. 21 



latin ^ condyle is of diverse form (cf. v. vi. x, 2), but usually 

 lias a convex or flat facet. The rami are united anteriorly 

 sometimes by symphysis, generally by ligamentous fibres : 

 tlie lower border of tlie symphysis is in Bimana alone 

 curved forwards and upwards (cf. ii, 1). The Sphenoid, as 

 above said, coalesces early with the occipital ; the size of the 

 wings varies ; the pterygoid processes sometimes remain 

 separate tbroughout life (cf. xv.) ; sometimes coalesce with 

 the surface of the Palatal bones. The separation of the body 

 of the Sphenoid into two parts {vide Introduction) as seen in 

 the Human embryo persists in most Mammals for the whole 

 of life. The Ethmoid is more largely developed in this 

 than in the other classes of Yertebrata, and here alone de- 

 serves the name which it has received in human anatomy, 

 from its perforated upper surface, or cribriform plate : in 

 very few Mammalia (cf. i. ii.) is the smooth lateral plate 

 forming the inner wall of the orbit (lamina papyracea) 

 present. The Inferior Turbinate bones seem to be present in 

 all Mammalia. The internal surface of the cranium presents a 

 cavity which, as in Aves, is entirely occupied by the brain, 

 and is thus the cast of its surface ; in Man it may be 

 divided into a posterior, middle, and anterior region, which 

 do not lie in the same plane, the posterior (cerebellar) being 

 the lowest : in other Mammalia these regions are less obvi- 

 ously distinct from each other, and lie more at the same 

 height. The depressions for the lodgement of the cerebrum 

 and cerebellum are sometimes separated by a bony tentorium, 

 prolonged inwards from the posterior part of the parietal 

 bones (cf. vi. viii, 1. xi.) and the superoccipital. 



II. The Vertebral Column. The articular surfaces at each 

 end of the well ossified centrum of a Mammalian vertebra are 

 generally flat : they are however sometimes cup- shaped 

 behind and spheroidal in front* (cf. x, 2.). This was also 



Opisthococlian centrum. 



