CHARACTERS OF MAMMALIA. $13 



mal to form a " furculum," as in Birds ; but in the Monotremes 

 they unite with an " interclavicle " placed in front of the ster- 

 num. 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 prehension. The 

 Cetacea, the Hoofed Quadrupeds ( Ungulata), and some of the 

 Edentata, have no clavicles. Most of the Carnivora and some 

 Rodents possess a clavicle, but this is imperfect, and does not 

 articulate with the top of the sternum. The Insectivorous 

 Mammals, many of the Rodents, the Bats, and all the Quadru- 

 mana, have (with man) a perfect clavicle articulating with the 

 anterior end of the sternum. 



The humerus, or long bone of the upper arm {prachium), is 

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

 the anterior limbs are converted into swimming-paddles. In 

 many Maraatials, as in the Monkeys, and Fdidm (constituting 

 the most typical group of the Carnivora), the median nerve and 

 brachial or ulnar artery are protected on their way down the 

 armb'y a canal placed a little above the elbow, and formed by 

 a process — the " supra-condyloid " process — ^which is some- 

 times present in man as an abnormality. 



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 

 anchylosed towards their distal extremities. In the flying 

 Mammals or Bats alone is the ulna ever altogether absent. 

 The fore-arm attains its greatest perfection in man, in whom 

 the radius can rotate upon the ulna, so as to allow the back of 

 the hand to be placed upwards or downwards, these movements 

 being known respectively as "pronation" and "supination." 

 In the Monkeys only is there any approach to this power of 

 rotation. 



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 bojies, 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 toes only, there are two 

 metacarpal bones in the embryo ; but these are anchylosed to- 



