134 VERTEBRATE ZOOLOGY 



cavity. The former is very much the larger and contains the liver, 

 the intestine, and most of the viscera ; it is lined by a membrane 

 called the peritoneum. The pericardial cavity contains only the 

 heart and the roots of the great blood vessels; it is formed by 

 a membrane called the pericardium. 



It will be observed that no abdominal muscles are present, which 

 in other land vertebrates form the ventral and lateral walls of the 

 abdomen ; this feature is correlated with the presence of the shell. 

 At the forward end are the large pectoral muscles ; they cover the 

 ventral portion of the pectoral girdle,— the bony structure which 

 supports the forelegs. At the hinder end are the large pelvic mus- 

 cles, which cover the pelvis,— the structure supporting the hind 

 legs. Both pectoral and pelvic girdles may be felt through these 

 muscles. Embedded in the muscles and the peritoneum may be 

 seen the yellow fat. Within the pericardium will be seen the heart. 



Embedded in the peritoneum are the two prominent abdominal 

 veins running in a diagonally longitudinal direction, and joined 

 together by cross veins. It will be remembered that in amphib- 

 ians a single median abdominal vein is present. 



Exercise 5. Make a semidiagrammatic sketch of the ventral aspect of 

 the animal, showing these organs, and carefully label all. 



With sharp scissors cut away the entire ventral portion of the 

 peritoneum and pericardium, together with the muscles attached 

 to them. Note carefully where the abdominal veins leave the 

 peritoneum and go to the liver. Do not cut the heart or any of 

 the other organs in the body cavity. 



Observe the organs as they lie in the body cavity in their natural 

 positions. Just back of and beneath the pectoral muscles is the 

 heart, and back of and at the sides of it is the large liver, the largest 

 organ present. The liver consists of a right and a left lobe joined 

 by a narrow bridge. Near the posterior edge of the right lobe may 

 be seen the green gall bladder. Partly or wholly beneath the outer 

 edge of the left lobe and joined with it by a mesentery is the 

 U-shaped stomach ; back of the liver are the coils of the intestine. 



Lift up the intestine gently and note the membranous mesentery 

 which joins it with the dorsal body wall and holds it in place. All 



