176 MORPHOLOGY OF THE ORGANS OF VERTEBRATES. 



of the anterior and posterior limbs being essentially identical. In 

 the fore limb there is in the region corresponding to the upper 

 arm (brachium) of man a single bone, the humerus; in the fore 

 arm (antibrachium) two bones, the radius on the anterior, the 

 ulna on the posterior side. In the wrist (carpus) there are 

 typically nine small bones, arranged in three series. The first 

 consists of a radiale on the radial side, an ulnare on the ulnar 

 side, and between these an intermedium. The second series 

 consists of a single centrale ; while the distal series is a row of 

 five carpales, numbered from one to five, beginning on the radial 

 (thumb) side. In the hand (manus) are recognized metacarpus 

 (palm) and digits (fingers). There are five metacarpal bones 

 in the palm, while the digits are composed of a number of bones 

 arranged in series (phalanges). The fingers are numbered 

 from one to five, beginning at the radial or thumb (pollex) side. 



In the hind limb the femur corresponds to humerus ; tibia 

 and fibula to radius and ulna respectively. The ankle (tarsus) 

 consists of tibiale, fibulare, intermedium, centrale, and five tar- 

 sales, and these are succeeded by metatarsals and phalanges, 

 which are numbered from one to five, beginning at the hallux 

 (large toe). 1 



These parts can be greatly modified, the chief changes con- 

 sisting of fusion or disappearance of some of these elements. 

 These alterations are usually more marked in the distal por- 

 tions, while those bones nearer the body are less subject to 

 modification. Occasionally bones may be added to these typi- 

 cal ones ; thus, there may be two centrales, and again, there 

 may be membrane (sesamoid) bones added to the wrist or 

 ankle. In cases where the details of reduction can be clearly 

 traced, it is found that the outer digits are the first to disap- 

 pear, the order of disappearance usually being i, 5, 2, 4. 



In human anatomy different names have been given to the 

 carpal and tarsal bones from those employed here ; and as in 

 the older works this nomenclature has been transferred to 

 other groups, the following table, which shows the usually 

 accepted homologies, may prove of value. 



1 The student is referred to special works for a discussion of those cases, like the frog 

 and the mammal Pedetes, which seem to indicate the existence of more than five digits. 



