706 MAMMALIA. 



as a rule present in Mammals which grasp or climb or 

 burrow. 



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

 forearm 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. 



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 little 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 hand is borne by the expanded end of the 

 radius. 



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, viz. : 



FIRST \ Ulnare or Intermedium or Radiale or 



Row / Cuneiform. Lunar. Scaphoid. 



Cent rale. 

 Carpal e 3 Carpale a Carpale j 



~\ Carpale 5 and 4 

 SECOND I Qr 



J Unciform. Os magnum. Trapezoid. Trapezium 



In Mammals the fourth and fifth carpals are never represented by 

 two distinct bones ; 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 con- 

 sists 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, 



