190 Anatomy of the Rabbit. 



3. In the mesenterial small intestine the following features may 

 be identified: 



(a) The lighter coloration, due to the thicker wall and. greater 

 vascularity, of the first or duodenal portion, thus distin- 

 guished as the jejunum (intestinum jejunum). 



(b) The darker coloration, due to the thinner wall, which allows 

 the contents to show through, and. diminished vascularity of 

 the terminal or caecal portion, thus distinguished as the 

 ileum (intestinum ileum). The two portions are not 

 distinctly separable. The circular folds (plicae circulares), 

 or valvulae conniventes, of the mucous tunic, which in many 

 mammals contribute to the thickness of the wall in the 

 duodenum and. jejunum, are, in the rabbit, not definitely 

 expressed. 



(c) The mesentery, the peritoneal support of the mesenterial 

 small intestine, is distinguished in its major portion by its 

 broad frill-like character, which allows great freedom of 

 movement to this portion of the digestive tube. Its terminal 

 portion, however, beginning at a point where the intestine 

 turns sharply forward on its way to the caecum, is adherent 

 to the mesocolon. 



(d) The mesenteric lymph glands (lymphoglandulae mesen- 

 tericae) are aggregated at the dorsal root of the mesentery, 

 where they form a compact mass surrounding the base of the 

 superior mesenteric artery. 



(e) The wall of the sacculus rotundus shows externally a fine 

 hexagonal pattern on account of the presence in it of a large 

 number of lymph follicles. Similar structures, forming oval 

 areas about 3 mm. in diameter and 5 mm. in length, may be 

 found along the intestinal wall (aggregated lymph nodules 

 of Peyer). 



(f) The finger-like processes, or villi, of the mucous tunic of the 

 small intestine may be seen by making an incision of the 

 wall and examining its internal surface. A small portion of 

 the wall may be excised and examined under water. 



4. Trace the course of the large intestine, beginning at the 

 sacculus rotundus, as follows: 



