124 ESSENTIALS OF ZOOLOGY 



pelvis and ends by joining the colon of the large intestine near the 

 right hip bone. Its first turn behind the stomach is the duodenum 

 and takes the shape of an inverted J turned backwards, to give a 

 short ascending limb from the stomach and a long descending limb 

 proceeding posteriorly. The pancreas, which is a branched (often 

 divided), thin gland, is held in the gastroduodenal mesentery. It fol- 

 lows the curve of the duodenum extending posteriorly and to the left 

 into the gastrosplenic mesentery. The pancreatic juice, which it pro- 

 duces, is collected by numerous, small, paired pancreatic ducts. The 

 ducts join the distal portion of the bile duct which enters the duo- 

 denum. Posteriorly the duodenum continues into the jejunum whose 

 boundaries are not very clearly defined anatomically but more readily 

 distinguished in histological studies. The ileum is the rather tightly 

 coiled portion which extends to the large intestine. The contents of 

 the ileum at this point pass through the ileocolic valve which com- 

 municates with both the colon (large intestine) and cecum. The 

 latter is a broad, curved sac on the right side of the abdominal cavity 

 and is about an inch to an inch and one-half in length. It occupies 

 the position of the vermiform appendix of man. This blind sac serves 

 as a cavity for the storage of partially digested food and fecal matter 

 in the rat. The cecum and ileum join the colon or large intestine 

 in its ascending portion. This part extends anteriorly to the region 

 of the stomach where it crosses to the middle of the cavity or beyond 

 as the transverse colon, turns posteriorly, and continues as the de- 

 scending colon. The rectum is the continuation of this portion of the 

 colon through the pelvis, and it terminates externally at the anus. 

 The fecal matter forms pellets and the masses of these pellets in the 

 colon infiuence the shape of certain portions of it. 



Glands Associated With the Digestive System 



Salivary Glands. — The parotid gland is a rather loosely organized 

 but conspicuous structure extending from the ventrolateral surface of 

 the neck to a position around the base and behind the ear. Its pos- 

 terior extremity reaches the shoulder, covering the outer half of the 

 clavicle. The parotid duct (Stenson's duct) is formed by the union 

 of three branches and proceeds across the masseter muscle to enter 

 the mouth through the cheek just opposite the upper molar teeth. 

 The submaxillary glands are large, elongated, and located on the ven- 

 tral surface of the neck. They are in contact with each other along 



