554 MAMMALS. 



scapula and the sternum. The triangular scapula has a 

 prominent external ridge or spine, continued ventrally into 

 an acromion with a long metacromion process. The scapula 

 is usually strong, and the clavicle is usually present in 

 mammals which grasp or climb or burrow. 



The fore-limb consists of an upper arm or humerus, a 

 fore-arm of two bones— the radius and the ulna, a wrist or 

 carpus, five palm-bones or metacarpals, and five digits with 

 joints or phalanges. 



The head of the humerus works in the glenoid cavity formed by the 

 scapula and the coracoid process. 



When the arm of a mammal is directed outwards at right angles to 

 the body, with the palm vertical and the thumb uppermost, the thumb 

 and the radius are in a preaxial position, the httle finger and the ulna are 

 in a postaxial position. But in the normal position of the limb in most 

 mammals,, the radius and the ulna cross one another in the fore-arm, so 

 that the preaxial radius is external at the upper end, internal at the 

 lower end. 



The typical mammalian wrist or carpus consists of two rows of bones, 

 with a central bone between the two rows. In the rabbit all the bones 

 — nine in number — are present. 



Ulnare or Cuneiform. Intermedium or Lunar. Radiate or Scaphoid. 

 Centrale. 



Carpale 5 and 4 Carpale 3 Carpale 2 Carpale i 



or or or or 



Unciform. Magnum. Trapezoid. Trapezium. 



In Mammals the fourth and fifth carpals are always fused ; the 

 centrale is often absent. In the tendons of the flexor muscles there 

 are often two sesamoid bones, of which the ulnar is called the 

 pisiform. 



In the rabbit there are five metacarpal bones and five digits, each 

 with three phalanges except the thumb or pollex which has but two. 



The pelvic girdle is articulated to the backbone, and bears 

 externally a cup-like socket or acetabulum in which the 

 head of the thigh bone works. Each half of the girdle — 

 forming what is called the innominate bone — really consists 

 of three bones which meet in the acetabulum. The dorsal 

 bone or ilium, which corresponds to the scapula, articulates 

 with the sacral vertebrae ; the pubis — the anterior of the two 

 lower bones— unites with its fellow on the opposite side in 

 the pubic symphysis; the two ischia, which correspond to 

 the coracoids, extend backwards, separated from the pubes 

 by the large obturator foramen, and expand into posterior 

 tuberosities. The ischia of mammals may touch one another 



