SQUIRREL MONKEYS 559 



are enormously enlarged and cavernous, while the jaw — in order 

 to accommodate and protect these various structures — is unusually 

 large and deep. The Howlers are furnislied with a fully pre- 

 hensile tail. The thumb is present. They are described as 

 being tlie most hideous in aspect of the American Monlveys, and 

 of the lowest intelligence, with which latter characteristic is 

 associated a less convoluted brain than in Ateles, for example. 

 The noise produced by these Monkeys is audible for miles, and 

 is said not to ])e due to emulation, i.e. not to be comparable to 

 singiny; or talkintj,- but to serve to intimidate their enemies. 

 The story told of these and otlier Monkeys with prehensile tails, 

 that tliey cross rivers by means of a bridge of intertwined Monkeys, 

 is apparently devoid of trutli. Tliere are six species, which are 

 Central and South American in range. 



The Squirrel Monkeys, genus Chrysothrix, are small creatures 

 with a long head, the occiput projecting. Their tail, though long, 

 has no naked area at the extremity and is non-prehensile. It is 

 a remarkable fact that the proportions of tlie cranium as compared 

 with tlie face are greater, not only tlian in other Monkeys, but 

 than in Man himself. The thumb is short, but not so short as 

 in the Spider Monkeys. The cerebral hemispheres are very 

 smooth ; but, as already remarked, this is a matter of size, and 

 not of low position in the series. It may appear at hrst sight 

 that this statement contradicts the one made concerning the 

 Howlers. But the latter are large Monkeys, and therefore ought, 

 so to speak, to have a more complex brain ; but they have not. 

 Like so many of the American Monkeys, tlie Squirrel ]\Ionkeys 

 are gregarious, and, in spite of tlieir tails, arboreal. They are 

 largely insect -feeders, and also catch small birds and devour 

 eggs. There are four species, of which C. sciicrea is the connnonest, 

 and is constantly an inmate of the Zoological Society's Gardens. 

 Humboldt asserted of it that when vexed its eyes filled with 

 tears ; but Darwin did not succeed in seeing this very human 

 expression of an emotion. 



Callithrix is a genus not far removed from the last, and, like 

 it, occurs ]joth in Central and in South America. It is chiefly 

 to be distinguished from Chrysothrix by the non-extension back- 

 wards of the head, and by the more furry character of the tail. 

 The lower jaw is rather deep, as in the Howlers ; but there is 

 not, or there has not been discovered, a howling apparatus like 



