122 Anatomy of the Rabbit. 



V. THE INTESTINES. 



The posterior portion of the digestive tube, or that portion extending 

 from the pyloric aperture of the stomach to the anal aperture, is divisible 

 into two main parts, not wholly distinguishable in calibre, namely, the 

 small intestine (intestinum tenue), and the large intestine (intestinum 

 crassum). Both are greatly elongated and convoluted. In examining 

 them care must be taken to avoid injury to the bloodvessels and me- 

 senteries, especially the dorsal attachments of the mesenteries, in which 

 the chief plexuses and related ganglia of the sympathetic system will 

 afterwards be traced. 



For the general relations of the intestines and mesenteries see pp. 

 41, 50. 



1. Beginning at the pylorus, trace the course of the small intestine, 

 as follows: Its first portion, the duodenum, forms a U-shaped loop 

 lying on the dorsal wall of the abdominal cavity to the right of the 

 vertebral column. The end of this loop, when traced from the right side, 

 disappears in the peritoneum and may then be picked up in a forward 

 position on the left side of the mass. This point marks the beginning of 

 the second portion, the mesenterial small intestine (intestinum tenue 

 mesenteriale), w^hich may be traced to its termination on the greatly 

 enlarged caecum. The connection with the caecum is through a rounded 

 semi-expanded sac, the sacculus rotundus. The terminal portion is 

 somewhat more difficult to follow on account of the adhesions of its 

 peritoneum with that of the large intestine. 



2. Examine the divisions of the duodenal loop and related structures, 

 as follows : 



(a) The superior, descending, transverse (horizontal), and as- 

 cending portions of the duodenal loop. 



(b) The common bile duct, opening on the dorsal wall of the 

 superior portion. 



(c) The mesoduodenum, a fold of peritoneum joining the various 

 parts of the loop. 



(d) The pancreas (Fig. ,3 B, p. 11). Its principal portion is here 

 seen as a diffuse brownish mass lying in the mesoduodenum. 

 Its duct (d. pancreatis) opens into the posterior portion of 

 the ascending limb. 



(e) The superior pancreaticoduodenal artery, a branch of the 

 gastroduodenal (see p. 119), passes backward on the first 

 portion of the descending limb. 



(f) The inferior pancreaticoduodenal artery (a. pancreaticoduo- 

 denalis inferior), a branch of the superior mesenteric (p. 125), 

 enters the mesoduodenum from the left side and supplies the 

 major portion of the loop. An anterior branch an- 

 astomoses with (e). 



