horyngeal pouch 



stomach 



liver 



gall bloddei 



yolk stalk (umbilicus) 

 allantoic stalk _ 



yolk stalk (umbilicus 



gall bladder 

 small intestine 



gastrohepatic ligament 

 falciform ligament 



spleen 



arrow through epiploic 

 foramen 



greater omentum 

 arge intestine 



small intestine. 



appendix 



Figure 9-1. Three stages in the development of the digestive tract of a mammal as seen in ventral 

 view. (After Patten, 1946) 



armadillos, while Hyrax has several caecal pouches along 

 the large intestine, including a pair of lateral diverticula. A 

 caecum is lacking in some mammals — hippopotamus, the 

 shrew Talpa, some bats, and bears. 



The large intestine curves forward on the right side of the 

 body, as the ascending colon; turns across to the opposite 

 side anterior to the general mass of the small intestine as 

 the transverse colon; and extends posteriorly as the de- 

 scending colon. From here it extends as the sigmoid colon 

 (man) to the midline rectum, which reaches to the anus. 

 Either the small intestine (cat, rat, man) or the large intes- 

 tine (pig) can be quite lengthened and spirally coiled. In 

 some bats and a few primates (Pin-Tailed Tree Shrew — Fig- 

 ure 9-2), the colon is short and straight. 



The monotremes agree with this general picture (Figure 

 9-3). The liver has several lobules that belong to the basic 

 right and left lobes. The gall bladder lies to the right of the 

 ventral midline. In Ormlhorhynchiis the stomach is sac-like 

 and has no gastric glands. Its lining is like that of the esoph- 

 agus (Figure 9-5). The pyloric opening is to the right of the 

 esophageal entrance and there is no pyloric valve. The 

 spleen is very large, extending from the mesentery above 

 the stomach posteroventrally and medially through bifur- 

 cate lobes to the posterior end of the body cavity. There is a 

 frilled greater omentum extending back from the stomach 

 between the coils of the gut and the spleen. 



The first part of the duodenum, perhaps the pyloric sec- 

 tion of the stomach, is thick-walled, with a horny papillate 

 lining and Brunner's glands in the submucosa. Since Brun- 



esophagus 



bile duct 



pleen 



stomach 



Figure 9-2. Ventral view of the digestive tract of a Pen-tailed Tree 

 Shrew, PWocercus. (After LeGros Clark, 1926) 



254 



THE VISCERA 



