68 THE LOW ER PRIMATES 



as far-distance receptors. The adiustment of ocular movement is as yet 

 so incomplete that the animal has not learned the many advantages arising 

 from a more exact stereoscopic vision for objects near at hand. Ocular con- 

 vergence brings the visual axes into such a position as to make possible the 

 more discriminating scrutiny of objects near the animal. It secures the more 

 exact effects of perspective and proportion characteristic of complete binocu- 

 lar vision. The relatively small size of the oculomotor nucleus in lemur 

 indicates an imperfectly developed binocular vision, while the lack of internu- 

 clear commissures implies that the muscles of the two eyes have not as yet 

 acquired the intimate intermuscular cooperation characteristic of animals 

 which have developed a high degree of binocular fusion and stereoscopic 

 vision. 



Another feature is the appearance of the red nucleus (NRu), a col- 

 lection of nerve cells in which at least two great systems ot fibers receive 

 relay. One of these systems is especially concerned in the efferent conduction 

 of impulses arising in the cerebellum and destined for distribution in the lower 

 levels of the axis. The nucleus ruber (NRu) in lemur is a relatively small 

 structure. Its size is in proportion to the correspondingly small number 

 of fibers forming the superior cerebellar peduncle. This small red nucleus sig- 

 nifies a limited functional capacity for the distribution of impulses essential 

 to the coordinative control, more particularly the coordinative control of 

 complex motor reactions in the upper and lower extremities. 



The two cerebral peduncles (CP) extend along the ventral surface 

 and are becoming more divergent as each approaches its corresponding 

 cerebral hemisphere. At the basis of the peduncle are the collected fibers of 

 the pyramidal system and also of the pallio-pontile system. Immediately 

 dorsal to these bundles of fibers is an extensive mass of gray matter, the 

 substantia nigra (Sbn), the significance of which has already been dis- 

 cussed in connection with the control of certain automatic associated move- 



