62 THE HUMAN BODY 



Fore and Hind Limbs. Each of these contains thirty bones, and 

 their arrangement is very similar. This is clearly seen in the 

 figures (34 and 35) , and is also brought out in the following table 

 in which the bones of the extremities are enumerated. 



Fore Limb Hind Limb 



a. Humerus, upper arm. Femur, thigh. 



6. Ulna, large bone of forearm. Tibia, shin bone. 



c. Radius, smaller bone of forearm. Fibula, small bone of calf. 



d. 8 carpals, wrist. 7 tarsals, heel and upper instep. 



e. 5 metacarpals, hand. 5 metatarsals, lower instep. 



/. 14 phalanges, fingers and thumb. 14 phalanges, toes (2 in great toe, 3 



(2 in thumb, 3 in each finger). in others). 



g. Patella, knee-cap. 



In general the bones of the hind limb are larger and stronger 

 than the corresponding ones of the fore limb; the femur is the 

 longest bone in the body. The phalanges, however, are smaller 

 in the foot than in the hand. The tarsals are one less in num- 

 ber than the carpals because one of the tarsal bones, the astragalus 

 (Fig. 38, To), is composed of two bones which have united into one. 

 A structure of the arm corresponding to the patella is the olecranon 

 process of the ulna which can be felt at the back of the elbow; in 

 early life this is a separate bone. 



The differences in structure between fore and hind limb corre- 

 spond to differences of function; the fore limb being a prehensile 

 organ is capable of great freedom of motion; the hind limb, which 

 is a supporting and locomotor organ, is adapted rather to main- 

 tain the weight of the body and to execute the movements of 

 walking and running to advantage. The special adaptation of the 

 arm to its purpose is seen particularly in three things: 1, the com- 

 paratively flexible attachment of the pectoral girdle to the axial 

 skeleton (Fig. 36), an attachment composed wholly of muscle and 

 ligament except where the inner ends of the clavicles articulate 

 with the sternum ; 2, the rotation of the radius over the ulna, an 

 arrangement which increases very greatly the flexibility of the 

 hand; 3, the articulation of the thumb, which is of such a sort as 

 to allow it to be opposed to any of the fingers, thus enabling the 

 hand to manipulate small objects without difficulty. The leg, on 

 the other hand, is characterized by much greater firmness, which 



