22 THE FROG CHAP. 



of the heart are two thin-walled transparent sacs (r. 

 Ing, I. Ing) with a honeycombed surface, the lungs. 

 Their appearance varies very much according to their 

 state of distension. When full of air they are about 

 two inches in length in a full-sized frog, and protrude 

 freely as soon as the abdomen is opened : when empty 

 they hardly show urtless the liver is turned aside. 



Emerging from beneath the left lobe of the liver 

 (beneath in the present position of the animal, actually 

 above) is a wide whitish tube (Fig. 3, st), which almost 

 immediately turns to the right (the frog's right, not 

 yours), so as to form a U-shaped bend (st, dm). This is 

 the stomach, which is connected with the pharynx by a 

 short tube called the gullet or oesophagus (compare Fig. 7, 

 gul, st), and which varies considerably in size according 

 to whether it is empty or distended with food. The 

 stomach becomes continuous with a narrower tube, the 

 first part of which (dm) passes forwards parallel with 

 the stomach, thus forming the narrow limb of the U, 

 while the rest of it (s. int) is thrown into a rather com- 

 plex coil. This tube is the small intestine ; the part in 

 immediate connection with the stomach (dm) is distin- 

 guished as the duodenum and the coiled part as the ileum. 

 Between the stomach and duodenum, in the bend of the 

 U, is a small yellowish-white body of irregular form, 

 the pancreas (Figs. 7, pn, and 18, P). 



The stomach and intestine are kept in place and 

 suspended to the dorsal wall of the body-cavity by a 

 delicate membrane, the mesentery (Fig. 5, mes), which is 

 folded in correspondence with the various coils. As we 

 shall see, the mesentery is really a portion of a thin, 

 moist membrane, the peritoneum, with which the body- 

 cavity is lined. 



The small intestine becomes continuous, posteriorly, 

 with a much wider tube (Figs. 3 and 7, ret], lying against 



