832 MAN 



stereoscopic vision. The reticular lorniation (Ref) is now much reduced 

 in size. There has emerged Ironi it a large circular nuclear mass, the nucleus 

 ruber (NRu). This nucleus shows a distinct increase in size compared 

 with the lower and intermediate primates and is even larger than in 

 the great anthropoids. Functionally it serves as a rela\ in the transmis- 

 sion of impulses mainly arising in the lateral lobes of the cerebellum. It may 

 also be the case that some fibers from the cerebellum are relayed in this 

 nucleus to pass cephalad into the interbram or e\en the endbrain. The 

 marked increase of the nucleus in the human brain is important as bearing 

 upon the increment in coordinative control already indicated in the size 

 of the lateral lobes of the cerebellum. 



Ventral to the reticular formation is a massive aggregation of nuclear 

 substance, the substantia nigra (Sbn ). Whatever may be the final opinion 

 concerning the functional significance of this large mass of gray matter in 

 the midbrain, it unc|uestionabIy manifests a progressive increase in size 

 and definition in the primates. Ventral to the substantia nigra is the 

 collection of fibers constituting the cerebral peduncle 1 C P ). These peduncular 

 fibers provide lor all those intricacies oi motor activity essential to the 

 life of the hunter m the use and the contrivance ol his weapons and 

 implements. They serve the expression of man's abilities as agriculturalist, 

 home-buildi'r, artisan and artist. Without these connections none of the 

 activities characteristic ol human society and cultural organization would 

 be possible. It ma\ be ciuestioned, thcrclorc, \\li\ these structures, denoting 

 such preeminent achit'\t'meiits in man, lia\e an\ representation whatsoever 

 in aj)es and lowtT mammals. It is, ho\\c\i'r, not the mere presence of these 

 neokinetic (ibers rejjrcsented m the cerebral pt'duiicK' w Inch gives them their 

 significance. They have a long mammalian history. In which their linal expan- 

 sion in the human bram displays this critical surplus over and above their 

 primitive, fundamental de\elo|)nient. 



" " 'J ' J (.,.. ; 



