650 



CHORD AT A. 



the brain (fig. 649, c). They have a single pair of pectoral 

 mammae, uterus simplex, and a discoidal placenta. The dentition 

 is essentially the same throughout; in the Platyrrhinae f Jf |, in the 

 Ilapalidse ffff , in the Catarrhinse and in man fff|. Yet there is 

 a tendency to variation, since in the chimpanzee and in man the 

 third molar (wisdom tooth) is in process of degeneration, while in 

 the orang a fourth molar often occurs. In all the molars are 

 bunodont. 



The skeleton of the hand and foot has played an important 

 role in classification. As in the lemurs and opossums, the thumb 

 and great toe can be opposed to the other digits, so that an ape can 

 grasp objects with either hand or foot. In man this opposability 

 of the thumb is increased, but that of the great toe, in consequence 

 of the upright position, is only retained to a slight degree by chil- 

 dren and primitive people. On this peculiarity rest the names often 

 given of Bimana, for man, and Quadrumana, for the apes and 

 monkeys. In contradiction of this it must be emphasized that the 

 apes do not have a hand, but rather a grasping foot, on the hinder 

 extremities. In the grasping foot (fig. 672) are the same bones, 



Fio. 672. Hand and foot of gorilla, c, capitatum; ca, calcaneus; CM, cuboid; 7i, ha- 

 matum ; i, lunatum ; me, metacarpals ; ??t, metatarsals ; n, iiaviculare ; p, pisi- 

 forrne; ph, phalanges ; s, scaphoid; t, triquetrum; <a, talus ; td, trapezoid ; tr, tra- 

 pezium ; /- F, digits ; 1-3, cuneiformia. 



similarly arranged and of about the same shape as in the foot of 

 man, while the musculature is essentially the same. On the other 



