22 THE ANIMALS AND MAN 



heart, ventricle, undergoes a contraction, forcing blood out 

 into the blood-vessels. This is followed by a relaxation of 

 the apex and a contraction of the basal portion, the auricle. 

 The heart is surrounded by a delicate semi-transparent sac, 

 the pericardium. The pericardium is filled with a watery 

 fluid, body-lymph, which bathes the heart. Note between 

 the lobes of the liver a small bladder-shaped transparent 

 organ of a pinkish color. This is the gall-bladder, a reser- 

 voir for the bile, the secretion from the liver. Separate the 

 lobes of the liver and note, beneath, the long convoluted 

 tube which fills most of the body-cavity. This is part of 

 the alimentary canal. The most anterior portion of the 

 canal, the gullet or oesophagus, leads to a large U-shaped 

 enlargement, the stomach. From the lower end of the 

 stomach there extends a long, slender, very much convo- 

 luted tube, the small intestine, which is followed by a much 

 larger one, the large intestine. This large intestine after 

 one or two turns passes directly back into the rectum, which 

 opens at last to the exterior through the anus. Note just 

 ventral to the rectum a large thin-walled membranous 

 sac. This is the urinary bladder which acts as a reservoir for 

 the secretion from the kidneys. Notice a many-branched 

 yellow structure with a glistening appearance, the fat-body 

 {corpus adiposum). Now push liver and intestine to one 

 side and note the pinkish sac-like bodies (perhaps filled with 

 air), the lungs. The lungs are paired bodies which open into 

 the laryngotracheal chamber. The toad takes air into its 

 mouth through its nostrils, and then forces it, by a kind of 

 swallowing action, through the laryngotracheal chamber 

 into the lungs. 



Now lift the stomach and note in the loop between its 

 lower end and the small intestine a thin transparent tissue. 

 This is a part of the mesentery, which will be found to sus- 

 pend the whole alimentary canal and its attached organs to 

 the dorsal wall of the body. Note in the loop of the stomach 



