SKELETON OF VERTEBRATA. 405 



bones of the pelvis, are the ilium, the ischium, 

 and the pubis. They all concur in the formation 

 of a large cup-like cavity, called the acetabulum, 

 which receives the head of the thigh bone (F), 

 constituting generally the largest joint in the 

 body. 



A single bone composes the first division of 

 each limb, both in the fore and hind extremities. 

 In the fore leg it is termed the humerus (H), in the 

 hind leg, the femur (F). The next division con- 

 tains two bones, placed parallel to each other ; 

 they are in the former, the radius (R), and the 

 ulna (u) ; in the latter, the tibia (T), atid fibula (f). 

 These are followed by a number of small, 

 rounded or cubical bones, collected together in 

 a group, which constitutes the Carpus (w), in 

 the fore leg, and the Tarsus (t), in the hind leg. 

 Next come a set of long cylindrical bones, com- 

 posing the metacarpus (m), in the former, and the 

 metatarsus (M), in the latter case. In the most 

 complete forms of developement these are always 

 five in number in each limb ; they are placed 

 generally parallel to each other, but are enve- 

 loped in one common covering of integument. 

 The Phalanges, or toes (z), are cylindrical bones, 

 continued in a line from each of the former : 

 they are generally three in number in each toe. 

 To the last joint, which is often termed the un- 

 gual bone, there is usually attached either a nail, 

 claw, or a hoof. Small detached bones are 



