400 MAMMALIA. 



outer aspect of the ribs, and much more developed than in the 

 Birds. The coracoid bone, which forms such a marked feature 

 in the scapular arch of Aves, is fused with the scapula, and 

 only articulates with the sternum in the Duck-mole and Echidna 

 (Monotremata). In all other Mammals the coracoid forms 

 merely a process of the scapula, and does not reach the top of 

 the breast-bone. The collar-bones or clavicles never unite in 

 any Mammal to form a "furculum," as in Birds : but in the 

 Monotremes they unite with an " inter-clavicle " placed in front 

 of the sternum. The clavicles, in point of fact, are not present 

 in a well-developed form in any Mammals except in those 

 which use the anterior limbs in flight, in digging, or in prehen- 

 sion. The Cetacea, the Hoofed Quadrupeds ( Ungulata), and 

 some of the Edentata, have no clavicles. Most of the Carni- 

 vora and some Rodents possess a clavicle, but this is imperfect, 

 and does not articulate with the top of the sternum. The In- 

 sectivorous Mammals, many of the Rodents, the Bats, and all 

 the Quadrumana, have (with man) a perfect clavicle articulat- 

 ing with the anterior end of the sternum. 



The humerus, or long bone of the upper arm (brachium\ is 

 never wanting, but is extremely short in the Whales, in which 

 the anterior limbs are converted into swimming-paddles. 



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

 cognisable, 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 rudi- 

 mentary. In the Cetacea the ulna and radius are anchylosed 

 together ; and in most of the Hoofed Quadrupeds they are an- 

 chylosed 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 Mammals from five to eleven. 



The metacarpus in man and in most Mammals consists of 

 five cylindrical bones, articulating 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 Ruminants and in the Horse. In the Ruminants, 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. 334, ca). In the Horse, in which 

 the foot consists 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- 



