Page:Laboratory Manual of the Anatomy of the Rat (Hunt 1924).djvu/89

Rh the food. The cardiac sac of the rodent, with its horny 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 morphologically 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 alimentary 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 comprises 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 centimeters 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