THE ALIMENTARY APPARATUS. . 235 



inclosed in and along the course of the mesenteries. In the in- 

 tervals of the coats they form three vascular nets, which supply 

 the serous,, muscular, and mucous coats. The veins accompany 

 the arteries and join the portal vein. 



The lymphatics follow the course of the superior mesenteric 

 vessels to enter the mesenteric glands. 



The nerves are derived from the solar plexus of the sympa- 

 thetic. 



THE LARGE INTESTINE. 



The large intestine is about five feet long and extends from 

 the ileum to the anus. 



It commences in the right iliac fossa, ascends through the 

 right lumbar and right hypochondriac regions, passes trans- 

 versely between the epigastric and umbilical regions to the left 

 hypochondriac region, where it descends through the left hypo- 

 chondriac, lumbar, and iliac regions, and through the pelvis on 

 its posterior wall to terminate at the anus. 



It consists of three divisions : 



1. Caecum, 



{Ascending, 

 Transverse, 

 Descending, 

 Sigmoid flexure. 



3. Rectum. 



THE C-^CUM is a blind pouch measuring about two and one- 

 half inches in every diameter, lying free in the right iliac region. 



It has opening into its lower back part the appendix vermi- 

 formis, and into its inner back part the ileum, guarded by the 

 ileo-caecal valve. 



The appendix vermiformis is a long, narrow, twisted tube, 

 the rudiment of the prolonged caecum in all mammalia. It ter- 

 minates in a blunt extremity. Its mucous membrane is contin- 

 uous with that of the cagcum, and contains many solitary glands. 



The ileo-ccecal valve, or valve of Bauhin, protects the opening 

 of the ileum into the cascum, and consists of two valve-like semi- 

 lunar folds of mucous membrane, strengthened by bands of cir- 

 c-ular fibres. The upper one is attached to the junction of the 

 ileum with the colon, the lower one to the junction of the ileiini 

 with the caecum. On each side where the folds coalesce, a 

 ridge of mucous membrane continuous for a short distance 

 around the canal, forming the frcena or retinacula of the valve. 

 The mucous membrane on either side of the valves corresponds 



