356 COMPARATIVE ANATOMY AND PHYSIOLOGY. 



as the lateral digits, with which some of them were 

 connected, have lost their function ; as the middle digits 

 have grown larger and thicker they have seized on the 

 carpal bones, and thereby gained " a better and more 

 complete support for the body." In some fossil forms 

 (Xiphodon, Anoplotherium), " the relation between the 

 carpal and tarsal bones, and the remaining two middle 

 metacarpals and metatarsals, remains just the same as 

 it was in the tetradactyle ancestor"; the digits that 

 remain do not, in other words, gain further support 

 from the carpal or tarsal bones. Forms in which 

 inheritance has been stronger than modification 

 have disappeared, while in those which have lived on 

 or left descendants, an adaptive modification 

 has been effected (W. Kowalevsky). 



As we ascend the scale of the Primates we find 

 an increasing tendency to throw the support of the 

 body on the hind limbs only ; thus, all the manlike 

 (anthropomorphous) apes are semi-erect ; the 

 Gibbon (Hylobates) uses the tips of his fingers much as 

 an active man uses a walking stick (Huxley), the orang, 

 the gorilla, and the chimpanzee, support themselves on 

 their knuckles. Man is erect, and, in correlation with 

 this position, the tuberosity of the os colds of the foot 

 is greatly broadened, the thigh and leg are in a 

 straight line, the pelvis becomes an open basin sepa- 

 rated by a wide space from the thorax, the vertebral 

 column takes on a marked S-shaped or sigmoid curva- 

 ture, the head is balanced on the atlas, and the spines 

 of the cervical vertebne, which have no longer to give 

 origin to powerful muscles, are reduced in size. Owing 

 to the monopoly of support enjoyed by the hind-limbs, 

 the fore limbs become free to serve as prehensile 

 organs, and in man, where there are no great canines 

 (as in male gorillas) to serve as organs of attack, it is 

 to the arms only that such an animal can look for 

 offensive or defensive organs. 



