262 VERTEBRATE ZOOLOGY 



inate bone is formed by the union of four bones : the ilium, which 

 forms its dorsal portion ; the ischium and pubis, which form its 

 ventral portion ; and the acetabular, a small bone between the other 

 three, which forms a part of the acetabulum. The ilium articulates 

 with the sacrum ; the ischium and the pubis are separated by the 

 obturator foramen, the former being the larger and more posterior 

 of the two. In most land vertebrates the pelvic girdle is composed 

 of three bones, the ilium, pubis, and ischium. 



Exercise 50. Make a drawing of the lateral aspect of the innominate 

 bone. 



The skeleton of the hind leg may be divided into a proximal, 

 a middle, and a distal division. The femur, or thigh bone, forms 

 the proximal division; it is a cylindrical bone, at the upper end 

 of which is the head, which articulates in the acetabulum. At the 

 side of the head is a large protuberance called the great trochanter ; 

 distally the bone ends in two projections, the condyles. 



On the anterior side of the distal end of the femur is a small, 

 independent membrane bone, which develops in a tendon and 

 forms the kneepan ; it is called the patella. 



The middle division of the leg is formed by the tibia and fibula. 

 The tibia is the larger and longer of these bones and alone artic- 

 ulates with the femur. Carefully note the relation of these two 

 bones to each other. 



The distal division is formed by the tarsus, or ankle, and the 

 pes, or foot. The tarsal bones are seven in number. The largest 

 is the calcaneum, or heel bone ; the large bone which articulates 

 with the tibia is the astragalus. 



The skeleton of the foot is composed of five metatarsal bones, 

 of which the first is rudimentary, and four digits, or toes. Each 

 digit has three phalanges. The first digit is wanting; the one 

 opposite the calcaneum is the fifth. 



Exercise SI. Make a drawing of the bones of the hind leg, reproduc- 

 ing the outlines of each exactly. 



The Axial Skeleton. The vertebral column consists of a succes- 

 sion of disklike vertebrae, which are closely joined with one another 



