MYCETES SENICULUS 223 



Situated above this latter nucleus are three important bundles of libers 

 superimposed one above the other: the superior cerebellar peduncle (Sep), 

 the fasciculus uncinatus of Russel (Tur), and the ventral spinocerebellar 

 tract (Gow). The trapezoid body (Trp) and mesial fillet (Mf) lie dorsal 

 to the pyramid (Py ). At the lateral apex of the corpus trapezoideum is the 

 superior olive (SO). The emergence from the axis of the seventh nerve in 

 its relation to the libers of the eighth nerve is clearly seen (N7 and N8). 



LEVEL THROUGH THE AHDDLE OF THE PONS VAROLII (fIG. 1 24) 



At the level through the middle of the pons Varolii a clearer conception 

 may be gained regarding the size and complexity of the pons. The stratum 

 superficiale is a dense and relatively broad bundle of fibers making its way 

 transversely into the middle cerebellar peduncle ( Mcp). Dorsal to this is the 

 stratum complexum containing the scattered bundles of the pyramidal system 

 (Py), some transverse fibers and the pontile nuclei (PN). In the most dor- 

 sal position is a fairly wide zone constituting the stratum profundum, the 

 transverse pontile libers of which also enter the middle cerebellar peduncle. 



Perhaps at no other level is it possible to obtain so comprehensive a view 

 of the animal's motor capacity from structural indices. The size of the pons, 

 including its transverse fibers and nuclear masses, indicates a degree of 

 cortical expansion in the cerebral hemisphere much above that attained by 

 lemur or marmoset. It is significant of an animal capable of considerable 

 coordinative control, one which has developed the lateral lobes of the cere- 

 bellum more than is to be observed in lower mammals. Because of this 

 development it has acquired control over the upper extremity such as is 

 commensurate only with animals possessing a more or less highly developed 

 hand. Nor is all of the prominence attained by the pons Varolii directly 

 ascribable to the increased demands in coordinative regulation of the upper 

 extrcmity.Thesedemandsmay be a primary incident or even an incentive to the 



