NECTURUS 83 



The Posterior Extremities. The pelvic girdle is different in shape 

 from the pectoral girdle. It consists of a large ventral plate, the 

 pubo-ischium, which lies between the hind legs in the ventral body 

 wall, and a slender rod on each side called the ilium, which extends 

 from the ventral plate upward to the spinal column. The pelvic 

 girdle, like the pectoral, is a paired structure and is composed of 

 three skeletal pieces on each side,— a dorsal piece and two ven- 

 tral ones. The dorsal piece is the ilium; it is a slender rod of 

 bone and cartilage. The ventral pieces are the pubis and ischium, 

 which form the pubo-ischium, the forward portion of that struc- 

 ture being the two pubes and the hinder portion the two ischia. 

 Near the base of the ilium, on each side, is the acetabulum, the 

 articular surface of the femur ; a short distance in front of this is 

 a small hole, the obturator foramen. The greater part of the pubo- 

 ischium is composed of cartilage ; a pair of bones is, however, pres- 

 ent in the hinder, or ischial, portion. 



The two ilia articulate with a single vertebra by means of its 

 ribs. This vertebra, which is called the sacrum, is usually the 

 nineteenth. In some cases the two ilia do not go to the same 

 vertebra but to two successive ones. 



Remove the thin layer of muscles which covers the ventral por- 

 tion of the pelvis and expose it. Be careful not to injure its an- 

 terior end, which runs to a point. Remove all the muscles in this 

 region and expose the spinal column and the ilium. Find the 

 articulation of the ilia with the sacrum ; disarticulate the ilia and 

 remove the pelvic girdle, with the legs, from the body. 



Exercise 20, Draw the pelvic girdle and carefully label its various 

 parts. 



Remove the muscles from the leg, but do not separate the 

 bones of the leg from one another. The skeleton of the leg is 

 composed of three divisions,— a proximal, a middle, and a distal. 

 The proximal division, or thigh, is a single bone, the femur, the 

 ends of which are of cartilage ; its proximal end articulates with 

 the acetabulum and forms the hip joint. In the middle division, or 

 shank, are two bones, the tibia and the fibula, the ends of which 

 are cartilaginous, the tibia being anterior, or preaxial, in position. 



