THE LARGE INTESTINE. 



921 



Vessels and Nerves. The jejunum and ileum are supplied by the superior 

 mesenteric artery, the branches of which, having reached the attached border 

 of the bowel, run between the serous and muscular coats, with frequent inoscu- 

 lations to the free border, where they also anastomose with other branches 

 running round the opposite surface of the gut. From these vessels numerous 

 branches are given off, which pierce the muscular coat, supplying it and forming 

 an intricate plexus in the submucous tissue. From this plexus minute vessels 

 pass to the glands and villi of the mucous membrane. The veins have a similar 

 course and arrangement to the arteries. The lymphatics of the small intestines 

 (lacteals) are arranged in two sets, those of the mucous membrane, and those of the 

 muscular coat. The lymphatics of the villi commence in these structures in the 

 manner described above, and form an intricate plexus in the mucous and submucous 

 tissue, being joined by the lymphatics from the lymph-spaces at the bases of the 

 solitary glands, and from this pass to larger vessels at the mesenteric border of the 

 gat. The lymphatics of the muscular coat are situated to a great extent between 

 the two layers of muscular fibres, where they form a close plexus, and throughout 

 their course communicate freely with the lymphatics from the mucous membrane, 

 and empty themselves in the same manner into the commencement of the lacteal 

 vessels at the attached border of the gut. 



The nerves of the small intestines are derived from the plexuses of sympathetic 

 nerves around the superior mesenteric artery. From this source they run to a 

 plexus of nerves and ganglia situated between the circular and longitudinal muscu- 

 lar fibres (Auerbach's plexus), from which the nervous branches are distributed to 

 the muscular coats of the intestine. From this plexus a secondary plexus is 

 derived (Meissners plexus), and is formed by branches which have perforated the 

 circular muscular fibres (Fig. 505). This plexus lies between the muscular and 

 mucous coats of the intestine. It is also gangliated, and from it the ultimate fibres 

 pass to the muscularis mucosse and to the villi and mucous membrane. 



THE LARGE INTESTINE. 



1 1 



The large intestine extends from the termination of the ileum to the anus, 

 is about five feet in length, being one- 

 fifth of the whole extent of the intestinal 

 canal. It is largest at its commencement 

 at the caecum, and gradually diminishes 

 as far as the rectum, where there is a dilata- 

 tion of considerable size just above the 

 anus. It differs from the small intestine 

 in its greater size, its more fixed position, its 

 sacculated form, and in possessing certain 

 appendages to its external coat, the appen- 

 dices epiploicce. Further, its longitudinal 

 muscular fibres do not form a continuous 

 layer around the gut. but are arranged in 

 three longitudinal bands or tcenice. The large 

 intestine, in its course, describes an arch, 

 which surrounds the convolutions of the 

 small intestine. It commences in the right 

 inguinal region, in a dilated part, the 

 caecum. It ascends through the right lum- 

 bar and hypochondriac regions to the under 

 surface of the liver ; it here takes a bend 

 (the hepatic flexure) to the left, and passes 

 transversely across the abdomen on the con- 

 fines of the epigastric and umbilical regions, 



to the left hypochondriac region ; it then bends again (the splenic flexure ), and 

 descends through the left lumbar region to the left iliac fossa, where it becomes con- 



FIG. 506. The caecum and colon laid open to 

 show the ileo-caecal valve. 



