MAN'S RELATIVES: THE PRIMATES 



481 



become relatively shorter and the legs stronger. In the more arboreal 

 chimpanzee the hands and feet are still long and narrow, with small 

 thumbs and great toes. In the more terrestrial gorilla the arm, hand, and 

 foot have become more like those of man, the thumb being larger and 

 more opposable, the foot shorter, and the weight of the body being carried 

 more on the sole of the foot and less on the outer edge than in other apes. 



The brain attains a volume of 500 

 to 600 cubic centimeters, which is 

 about half that found in the most 

 primitive men. The skull (Figs. 

 29.13, 30.4 to 6 and 13) is large but 

 low vaulted, and in older individuals 

 it develops bony crests on top and at 

 the rear for the attachment of the 



Fig. 29.11. An African chimpanzee, Pan 

 (= Anthropopithecus). (Courtesy American 

 Museum of Natural History.) 



Fig. 29.12. A large male gorilla of the moun- 

 tain species, Gorilla beringeri. (Courtesy 

 American Museum of Natural History.) 



huge jaw and neck muscles. There are prominent bony ridges above the 

 eyes (especially in gorillas); the nose is depressed and the muzzle prom- 

 inent. The canine teeth form projecting and interlocking tusks. The molar 

 teeth are quite similar to those of man ; but they are larger and somewhat 

 elongated from front to rear instead of being quadrate and are further 

 distinguished by having five cusps instead of the four cusps usual in 

 modern human teeth. In each jaw the teeth are set in a long narrow 

 U-shaped arch (Fig. 29.15), with the molars in parallel rows, while in 

 man the arch is shorter and broader, forming a parabola with the molar 

 rows divergent behind. The chimpanzee, the gorilla, and man are similar 



