278 



MAMMALIA. 



In the fore-arm of all Mammals the ulna and radius are 

 recognisable, but they are not necessarily distinct ; and the 

 radius, as being the bone which mainly supports the hand, 

 is the only one which is always well developed, the ulna 

 being often rudimentary. In the Cetacea the ulna and radius 

 are anchylosed together; and in most of the Hoofed Quad- 

 rupeds they are anchylosed towards their distal extremities. 

 The fore-arm is succeeded by the small bones which com- 

 pose the wrist or " carpus." 

 These are eight in number in 

 man, but vary in different Mam- 

 mals from five to eleven. 



The metacarpus in Man and 

 in most Mammals consists of 

 five cylindrical bones, articulat- 

 ing proximally with the carpus, 

 and distally with the phalanges 

 of the fingers. The most re- 

 markable modification of this 

 normal state of things occurs 

 in the Euminants and in the 

 Horse. In the Euminants, in 

 which the foot is cleft, and 

 consists of two perfect toes 

 only, there are two metacarpal 

 bones in the embryo ; but these 

 are anchylosed together in the 

 adult, and form a single mass 

 which is known as the " canon- 

 bone" (fig. 595, ca). In the 

 Horse, in which the foot con- 

 sists of no more than a single 

 digit, there is only a single 

 metacarpal bone, on each side of which are two little bony 

 spines — the so-called "splint-bones" — which are attached 

 superiorly to the carpus. These are to be regarded as rudi- 

 mentary metacarpals. In most of the other Ungulates there 

 are at least three metacarpals, and in the Elephants there 

 are five. 



B 



Fig. 595. — A, Fore-leg of the Horse: r, 

 Radius ; c, Carpus ; ca, Canon-bone ; p, 

 Splint-bone ; o, First phalanx or " great 

 pastern ; " 6, Second phalanx or " small 

 pastern ; " c, Ungual phalanx or " coffin- 

 bone." B, Fore-limb of a Deer : r, Radi- 

 us ; c. Carious ; ca, Canon-bone ; s, One 

 of the supplementary toes. 



