THE FROG 15 
is fastened by a thin membrane, the mesentery, to the dorsal 
body-wall. 
(b) The liver, already noticed, is a large dark-red organ partly 
covering the duodenum and stomach. How many lobes has it? 
On the dorsal side observe the gall bladder or bile sac which is 
usually filled with green bile. Observe the bile duct which 
extends from the gall bladder to the duodenum, and the various 
hepatic ducts which enter the bile duct from the liver. In a 
freshly-killed specimen, by gently pressing the gall bladder and 
forcing bile from it into the duct, the course of the bile duct may 
be more easily followed. 
(c) The pancreas, a flat, irregularly lobed yellowish organ lying 
between the stomach and the duodenum and stretching from the 
liver to the small intestine. The bile duct passes through it, and 
the pancreatic ducts empty into the bile duct. Look up the course 
of the bile duct in the human body; does it pass through the 
pancreas as in the frog? 
3. The lungs, two thin-walled sacs lateral and posterior to the 
heart; they lie dorsal to the liver and are usually hidden by it. 
Insert a blow-pipe into the glottis of a freshly-killed frog and 
inflate the lungs. 
4. The spleen, a round dark-red organ in the mesentery near 
the anterior end of the large intestine. 
5. The excretory system. (a) The kidneys, a pair of reddish, 
flat bodies lying next to the dorsal wall of the body, and sepa- 
rated from the body cavity by a thin membrane, the peritoneum. 
Expose a kidney by cutting through the peritoneum of one side 
only. If the specimen is a female, in order to expose the kidney 
it may be necessary to remove one ovary (described below) by 
cutting the membrane by which it is attached. Observe a yellow- 
ish band, the adrenal body, on the ventral surface of each 
kidney ; this corresponds to the suprarenal body of man. 
(b) The ureters emerge from the posterior fourth of each 
kidney on its lateral edge. They are slender, white tubes, one for 
each kidney, which converge as they pass posteriorly, and empty 
into the dorsal side of the cloaca. 
(c) The bladder, a slightly bi-lobed sac opening by a narrow 
neck into the ventral side of the cloaca. Insert a blow-pipe or 
