2l8 



THE LOWER PRIMATES 



accessory portions, i.e., the ventral accessory olive (VO) and the dorsal 

 accessory olive (DO). The significance of this increase I^oth in definition 

 and size of the olivary body may be understood in relation to the animal's 



FIG. I 20. MYCETES SENICULUS. LEVEL OF THE NUCLEUS AMBIGUUS. 



AMB, Nucleus Ambiguus; dt, Deiters' Nucleus; do, Dorsal Accessory Olive; cow. Dorsal Spinocerebellar 

 Tract; hel, Spino-olivary Tract of Helweg; ICP, Inferior Cerebellar Peduncle; 10, Inferior Olive; mf, Mesial 

 Fillet; nhv. Hypoglossal Nucleus; nfs. Fasciculus Solitarius and Nucleus; nsc, Nucleus of Schwalbe; nr, 

 Nucleus of Rolando; N12, Hypoglossal Nerve; pl, Posterior Longitudinal Fasciculus; pd, Predorsal Fas- 

 ciculus; PY, Pyramid; ref. Reticular Formation; rst, Rubrospinal Tract; spt, Spinothalamic Tract; trd, 

 Descending Trigeminal Tract; vo, Ventral Accessory Olive. [Accession No. 148. Section 155. Actual Size 

 13X6 mm.] 



need of more accurate coordination in the simultaneous movements of eyes, 

 head and hands for the new motor attainments acc[uired in consequence of 

 manual development. 



LEVEL OF THE NUCLEUS SUPPLYING MOTOR FIBERS TO THE LARYNX (fIG. I20) 



At this level, a noteworthy specialization appears in the more fixed por- 

 tion of the brain stem which throughout the primate series, generally speak- 



