Chapter V 



CALLITHRIX JACCHUS, THE MARMOSET, ITS BRAIN 

 AND BEHAVIOR 



Its Positiun amansi the Primates; Measureynents cutd Brain Indices; Surface 

 A})])earance of the Brain; Internal Structure of the Brain Stem in Cross Section 



Iow 

 -J 



OWEST amono; the Anthropoidea arc the Hapalidac or marmosets. 

 These animals belong to the group of new-world monkeys. They 

 ^M inhabit South and Central America. Their digits are for the most 

 part clawed, with the exception of the great toe which alone bears a Hat nail. 

 The tail is long, bushy and rmgcd, a condition characteristic of many of the 

 lower groups of mammals but not observed among the higher apes. Unlike 

 most of the South American monkeys, the tail of marmoset is not prehensile. 

 In size they are about as large as a small squirrel and are covered with a 

 thick silky fur. Although naturally timid, they readily become accustomed to 

 those with whom they are familiar in captivity. The female produces two or 

 three young at a birth and in this respect is unlike other Anthropoidea. In 

 facial appearance, in size and shape of head, the Hapalidae convey a much 

 more ape-like impression than do the lemurs. On the other hand, their spe- 

 cialization in limb, particularly with reference to the hand, seems hardly 

 so far advanced as in the Lemuridae. The eyes are much closer together and 

 separated by a flat, narrow nose, suggesting the possibility of some degree, 

 at least, of binocular vision, although it seems probable that even in this 

 respect, the animal's visual function has not attained a high degree of 

 difl'erentiation. 



On the whole, the marmosets, because of their very small size, seem but 

 retrograde steps in the dilTerentiation which culminates in the strikingly 



