156 THE STEUCTUEE OF THE HOESE. 



segment of both limbs has two bones lying side by 

 side — the radius and ulna in the fore limb and the 

 tibia and fibula in the hind limb. The joint by which 

 the proximal segment is attached to the correspond- 

 ing girdle is called " shoulder" in the fore limb, and 

 " hip " in the hind limb ; that between the first and 

 second segments is called the "elbow" in the fore 

 limb and the " knee " (the " stifle " in the horse) in 

 the hind limb (see the skeleton of the horse and man 

 in Frontispiece). 



The distal or third segment is of more complex 

 character. It constitutes in the fore and hind limbs 

 respectively the " hand " and " foot " of man, the fore 

 and hind "foot" of quadrupeds, or, in more precise 

 anatomical language, of general application to all 

 animals, the manus and the pes. Each of these con- 

 sists of a group of small bones at its proximal end, 

 forming the carpus or wrist in the fore limb and the 

 tarsus or ankle in the hind limb. Beyond these it 

 always has a tendency to divide up into a number of 

 rays, called digits, fingers, or toes (see Fig. 1, p. 15). 



Leaving out of consideration certain vestigial 

 structures which are held by some anatomists to in- 

 dicate the possibility of the former existence of a 

 larger number of digits, no known mammal has more 

 than five digits in each limb. For the convenience 

 of description the digits are distinguished by the 



