INTRODUCTION xv 



Some of the small Monkeys of the New World emit a whistling note, 

 often plaintive, but the most wonderful voices are those possessed by 

 the species of Alouatta in South America, and of Hylobates of the 

 eastern hemisphere. In these the throat is large and thick and the 

 larynx greatly developed. The basihyal is much enlarged and is ex- 

 panded into a bony capsule which is lined by a continuation of the 

 thyroid sac, and this peculiar formation enables the animal to produce 

 a volume of sound that can be carried, it has been estimated, for a 

 distance of three miles. 



The brain of the great Apes is slightly more than half the size of 

 that of Man. The Gorilla, like all of the Quadrumana, has the brain 

 fully developed before the permanent set of teeth are completed. At 

 that period the animal has not, of course, its full stature, and the skull 

 continues to grow with the animal, but the brain does not, the skull 

 becoming heavier and thicker in bone with broader and longer crest, 

 but the brain itself is stationary. *"The relative size of the brain 

 varies inversely with the size of the whole body, but this is the case 

 with warm-blooded vertebrates generally. The extreme length of the 

 cerebrum never exceeds, as it does in Man, two and a quarter times 

 the length of the basi-cranial axis. The proportions borne by the 

 brain to its nerves are less in the Apes than in Man as also is that borne 

 by the cerebrum to the cerebellum. In general structure and form 

 the brain of Apes greatly resembles that of Man. Each half of the 

 cerebrum contains a tri-radiate lateral ventricle, and though in some 

 LASioPYGiDiE the posterior cornu is relatively shorter than in Man, it 

 again becomes elongated in the Cebid^, and in many of the latter it is 

 actually longer relatively than it is in Man. The posterior lobes of the 

 cerebrum are almost always so much developed as to cover over the 

 cerebellum, the only exceptions being the strangely different forms 

 Mycetes, (Alouatta), and Hylobates, (Symphalangus), syndac- 

 TYLUS. In the latter the cerebellum is slightly uncovered, but it is so 

 considerably in the former. In Chrysothrix, (Saimiri), the posterior 

 lobes are much more largely developed relatively than they are in Man. 

 The cerebrtim has almost always a convoluted external surface. In 

 this group, however, as in mammals generally, a much convoluted 

 cerebrum is correlated with a considerable absolute bulk of body. 

 Thus in Hapale, (Callithrix), (and there only), we find the cere- 

 brum quite smooth, the only groove being that which represents the 

 Sylvian fissure. In Simia, (Pongo), and Gorilla, and Anthropo- 



*St. George Mivart, Encycl. Britan., 9th Ed., Article Ape. 



