Chapter VII 

 MVCETES SENICULUS, ITS BRAIN AND BEHAVIOR 



//,s' Position amonii the Primates; Measurements and Brain Indices; Surface 

 Aj)])earance oj the Brain; Internal Structure of the Brain Stem in Cross Section 



jT' II ^HE Cebidac arc in general much larger than the Hapahdae and 

 I more apc-hkc in appearance than the lemurs. The tail, although 

 11 , short in a few instances, is usually long and definitely prehensile. It 

 is not covered with hair at its extremity and in this part especially manifests 

 its prehensile characters. These animals vary considerably in size; some 

 species are but little larger than the marmoset, while the larger members of 

 the family are only a little smaller than some of the old-world monkeys. In 

 general they are about as large as a fox-terrier. The development of the tail 

 attains its highest degree of specialization in the spider monkey (Ateles) and 

 the woolly monkey (Lagothrix). In these Cebidae the tail is so much differen- 

 tiated in its prehensile function as to justify speaking of it as a Jijtb band. By 

 means of this fifth hand the monkey swings its way along among the 

 branches, procuring many advantageous positions of the body which enable 

 it to use both fore- and hindlimbs in the manner of hands. It can reach, 

 grasp and even hurl small objects by means of its tail. When not in use, the 

 tail is carried erect over the head. This highly specialized sensory organ adds 

 an important element to the behavioral organization of the animal, some 

 evidence of which must be reflected in the central nervous system. 



The howling monkeys constitute an interesting group of the Cebidae. 

 While they arc not possessed of a tail so highly differentiated as the spider 

 monkeys, this organ none the less has great efficiency in its prehensile 



