SKELETON. 



645 



cromion process. The scapula is usually strong, and the 

 clavicle is 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 



Fig. 281.— Rabbit's hind-leg. 



Fe. t Femur ; TV., third trochanter ; Ep., epiphysis at head of tibia 

 (Ti.) ; Fi., incomplete fibula ; C., calcaneum ; A., astragalus ; 

 int. , metatarsals. 



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

 joints or phalanges. 



The head of the humeius 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 



