THE LIMBS. 



303 



form the lower part of the extremities. In ruminants the 3rd 

 and 4th digits have become specialized ; the rest of the digits 

 have become reduced until only traces of them are left ; in rodents 



radius or tibia. 



radiate or tibiale. 

 carpal V. 

 meta-carp,.. 



ulna or fibula, 

 intermedium 

 ulnare orfibulare 

 carpal I. 

 centrale 

 carpal III. 



Pig. 246.— The Carpal Bones of a Tortoise. 



the hallux is vestigial. The hallux and pollux are the mammalian 

 digits most liable to undergo retrogression. In man, on the other 

 hand, the hallux and pollux find their greatest development. 



Comparison of the Tarsus and Carpus. — Both are the de- 

 rivatives of such a typical form as is shown in Fig. 246. In the 

 typical tarsus or carpus there occur the following bones : 



1. Radiale or Tibiale forms the scaphoid in the hand and 

 astragalus in the foot. 



os ealcis (fibulare) 

 os trigonum {intermedium) 

 astrag. (tibiale) 



cuboid(4.5tarsa/e)-J^ -scaphoid (centmle) 



Fra. 247.— The Os Trigonum and Bones of the Tarsus. 



2. Intermedium forms the semilunar in the hand ; in the foot 

 it is much reduced and usually unites with the astragalus to form 



