294 TOWARDS THE HUMAN FORM 



of the toes provided with nails resembling a hoof. They 

 would thus appear to have led up to the Ungulates, which 

 arrived eventually at walking only on the extremities of their 

 toes, and in whose limbs the highest degree of reduction of the 

 digits is attained. The arrangement of the carpal and tarsal 

 bones is subjected to the most remarkable modifications. These 

 bones are disposed in two rows. In the carpus the first row 

 comprises three bones : one of them, the scaphoid, articulating 

 with the radius, is also called the radiate, and another, the 

 cuneiform or pyramidal, articulating with the ulna, is there- 

 fore sometimes called the ulnare. Between the two there is 

 intercalated the intermedium or semilunar bone. The bones of 

 the second row are placed exactly in front of them : the radial 

 supports the trapezium and the trapezoid ; the intermedium the 

 os magnum, and the pyramidal the uncinatum or unciform 

 bone, which itself results from the union of the fourth and fifth 

 bone of this row. Each of these bones supports one digit only, 

 with the exception of the unciform bone, which is double and 

 supports two. Thus the bones of the digits and those of the 

 carpus are disposed as far as the bones of the forearm in 

 longitudinal series, in which each bone unites only with the 

 one preceding and the one following, and is free laterally. This 

 serial arrangement in the carpus is not particularly inconvenient 

 and has perhaps some advantages for animals with a heavy 

 tread, in whom the foot plants the whole extent of its inferior 

 aspect on the ground and is thus unembarrassed by 

 irregularities. On the other hand, it exposes fleet-footed animals 

 to the risk of dislocations, since at each bound the}' land 

 suddenly upon the end of the toe, which is the only part of the 

 foot to touch the ground. This arrangement is already modified 

 in the hind foot in the oldest plantigrade forms. There the 

 tibiale and intermedium are united to form the astragalus, which 

 articulates with the tibia ; the fibular e or peroneal, which 

 follows the fibula, develops particularly in the rear, and forms 

 the calcaneum or heel-bone ; a special bone, the navicular, 

 represents the os centrale of the Batrachians, and a free bone, 

 the pisiform, is perhaps the remnant of a sixth digit that has 

 always remained rudimentary. In front of the bones of the first 

 row are arranged the five bones of the second, of which three, 

 the cuneiform bones, remain free and two are united to form 

 the cuboid. The serial arrangement appears only after these 



