138 THE GENERAL ANATOMY OF THE CERCOPITHECIDAE [SECT. A 



and dividing usually above the level of the elbow joint. Thus 

 various types of the " high origin " of the radial and ulnar 

 offshoots are produced, and the arrangements are similar to those 

 found in many human foetuses before the end of the sixth month 

 of intra-uterine life. The radial and ulnar contributions to the 

 palmar arches are about equal in size in Cercopithecus, while in 

 the Cynocephalous monkeys the ulnar artery is the smaller of the 

 two and thus more primitive. In the lower limb, the deep branch 

 of the common femoral artery is less developed, i.e. it gives off 

 fewer important branches than in Man. In particular the A. cir- 

 cumflexa medialis may arise (with the A. obturatoria) from the 

 A. hypogastrica. A distinctive feature is the A. saphena which 

 runs from the thigh to the foot in a subcutaneous situation, and 

 ends mainly as a vessel perforating the second interosseous (meta- 

 tarsal) space. The A. poplitea is not pressed into the fold of the 

 knee (as in Man), and its position like that of the A. saphena 

 seems to be determined by the characteristic flexure of that joint. 

 The two plantar arteries are present, but small, the chief supply 

 to this part coming via the A. saphena through the second space 

 as described above. 



H. Nervous System, i. The Cercopithecidae possess a 

 brain conspicuous for certain details of specialization. 



Foremost among these, the large size of the corpus callosuin 

 may be mentioned. This character is not only expressive of the 

 increased mass of the neopallium, but it indicates particularly an 

 augmentation of the association areas of the cortex. The extension 

 of the latter is the more important character. But the boundaries 

 and extent of those areas are not evident until a variety of details 

 have been studied. The corpus callosum is easily exposed to view, 

 and since its limits are distinct, it has been placed in the fore- 

 ground here. 



The cerebellum has also increased in relative bulk and is nearly 

 as instructive as the preceding characters. 



ii. Examples of conditions apparently primitive, but with 

 better reason ascribed to degenerative changes, are insignificant 

 or absent. Where degeneration has taken place its effects are not 

 of this kind. 



