178 



THE LOWER PRIMATES 



in the cerebral cortex of the occipital lobe, it is probably true also that the 

 superior coliicukis maintains its primordial arrangement in the interest of 

 certain primitive and immediate rellex reactions in response to visual stimuh. 



FIG. »». MARMOSET. LEVEL OF THE SUPERIOR COLLICULUS. 

 CEN, Central Gray Matter; cp. Cerebral Peduncle; crx, Central Tegmental Tract; mf, Mesial Fillet; mob. 

 Mesial Geniculate Body; noc, Oculomotor Nucleus; nru. Nucleus Ruber; N3, Oculomotor Nerve; pd, 

 Predorsal Bundle; pl, Posterior Longitudinal Fasciculus; ref, Reticular Formation; sbn. Substantia Nigra; 

 sc, Superior Colliculus; spt. Spinothalamic Tract. [Accession No. 146. Section 167. Actual Size 10X6 mm.] 



In this particular, the case is similar to that of the inferior colliculus which 

 has apparently retained much of its primordial auditory function. The neces- 

 sity for quick, decisive motor responses as a reaction to visual stimuh on the 

 part of the marmoset must be obvious. Most of the animal's reactions to visual 

 stimulation resuh in very rapid movements of the head, eyes, neck and limbs. 



