THE DIGESTIVE SYSTEM 75 



the food. The cardiac sac of the rodent, with its homy 

 lining, is thought to be a storehouse for holding chewed food 

 pending gastric digestion. It has been suggested that the 

 dangers involved in feeding have led Rodents to develop 

 this thin-walled sac in which quickly procured food may 

 be stored. 



The intestine is the part of the alimentary canal in 

 which the digestion and absorption of food is completed. 

 It is an extensively coiled tube occupying a large part of 

 the abdominal cavity. It is physiologically and mor- 

 phologically divisible into two parts, the small and the 

 large intestine. The discussion of the mesenterial supports 

 will be deferred until after the description of the alimen- 

 tary canal itself. The length of the small intestine may be 

 about 70 centimeters, more than three times the length of 

 the animal from the tip of the snout to the base of the 

 tail. The large intestine, including caecum and rectum, 

 is about 20 centimeters long. The small intestine com- 

 prises the duodenum, jejunum, and ileum. 



The duodenum lies on the right side of the abdominal 

 cavity. It is approximately u-shaped, and is therefore 

 composed of three parts — a descending, a transverse, and 

 an ascending limb. The first joins the stomach at the 

 pylorus. From this attachment it turns posterodextrad 

 in a broad curve, and runs backward about four centi- 

 meters near the right abdominal wall. The transverse 

 duodenum is the sharp short curve at the posterior end 

 of the descending limb, connecting the latter with the 

 ascending limb. The latter passes forward along the right 

 side of the colon, and is connected by a mesentery with the 

 distal edge of the mesocolon. lii a preserved specimen the 

 duodenum is pinkish or slightly grayish in color. The 

 gross structure of the internal surface may be observed 

 to good advantage with a dissecting microscope if a fresh 



