50 , THE LOWER PRIMATES 



ventricle, is the trianiiular nucleus of Schwalhe (NSc), and lateral to this 

 a large-celled nucleus known as Deiters' nucleus (ND). Together they 

 constitute the vestibular area. Dispersed among the cells of Deiters' nucleus 



FIG. 26. LEMUR MONGOZ. LEVEL OF THE VESTIBULAR COMPLEX. 

 CTT, Central Tegmental Tract; dt, Deiterso-spinal Tract; gow. Ventral Spinocerebellar Tract; icp, Inferior 

 Cerebellar Peduncle; mf, Mesial Fillet; nd, Nucleus of Deiters; nfs. Facial Nucleus; nr. Nucleus of Rolando; 

 NSC, Nucleus of Schwalbe (Triangularis); n8. Auditory Nerve; pd, Predorsal Bundle; pl. Posterior Longi- 

 tudinal Fasciculus; py, Pyramid; ref. Reticular Formation; rst, Rubrospinal Tract; spt, Spinothalamic 

 Tract; trd. Descending Trigeminal Tract; tub, Tuberculum Acusticum. (Accession No. 147. Section 138. 

 Actual Size, 14 X 4 mm.] 



are many scattered bundles of nerve fibers representing essential connections 

 of this nucleus. The relative dimensions of the two vestibular nuclei to the 

 rest of the cross section are of especial internst. They provide a basis for 

 estimating the degree of balancing function possessed by the lemur, whose 

 life is spent primarily in the loftiest parts of trees and whose locomotion is 

 adapted to the constantly varying movements of the tree tops. The animal 

 is able to execute difficult locomotor feats with great precision and finds as 

 much security in its balancing under these most difFicult circumstances as 

 the quadruped does upon terra lirma. It is cjuite in keeping, therefore, with 

 the inherent behavioral requirements, to find the central representation of 



