TROGLODYTES GORILLA 665 



the hraiii stem is a characteristic of progressive clillerentiation and is espe- 

 ciall\ well eni|)hasizecl in the hi<z;her primates. 



Ill tlu' lateral wall ol the \'entriclc is a nuclear mass, tlii' most mesial 

 portion ol which rt'prescnts tlu' attenuated upper extremity of the nucleus 

 of GoII (NG). Arcuate hhers pass from it forwaixl and inward toward 

 the median raplu' to enter the mesial fillet (Mf). The adjacent nucleus 

 of Burdach (NB), as already indicated, is separated by a faintly dis- 

 cerned dorsal paramedian sulcus, and i)rescnts itself as a more or less scat- 

 tered a(z;gregation of nuclear substance. The outer portion of the nucleus of 

 Burdach is the nucleus ol Blunienau (NBI). In the gorilla it is especially 

 complex in arrangement and large in size. Occupyinga position \entral to the 

 nucleus ol Burdach is the substantia gelatmosa trigemini ( NR) now some- 

 ^vhat ol)scured by the crowding fibers which lorm the restiform body. 



In the lateral extremity of the central gray matter (Cen) is a 

 dense bundle ol fibers, somewhat oval in outline, the fasciculus solitarius 

 (Nfs), coming into relation with which are the entering fibers of tlu' 

 vagus nerve. The reticular formation occupies the central portion of 

 the section (Ref). It is crossed b\' man\ internal arcuate lii)ers taking 

 origin in the nucleus of Burdach and following a course which leads to 

 the ra[)he and the decussation of the mesial fillet (Mf ). Occupying the 

 most ventromesial portion of the section are the fibers of the pyramidal 

 system forming the pyramid (Py). The inferior olive (10), showing 

 not only an increment in \()hime but added complexity in its convolutions, 

 indicates to what extent there has been an increase in the control of 

 simultaneous movements of head, eyes and hand, and in the facilitation 

 of coordination of all skilled learned performances. This observation supports 

 the idea that the gorilla has made definite advances toward that ultimate 

 goal In which the hands arc eventually irced from direct participation in 

 locomotion. Such manual emancipation provides a means for exploring the 



