THE ABDOMEN 795 



Except in the case of the transverse colon, these are chiefly found 

 along the postero- internal taenia, but in the case of the transverse 

 colon they are principally met with along the postero-inferior 

 taenia. 



The circular fibres are thin and scattered over the sacculi, but in 

 the constrictions between them they become aggregated. Upon 

 the rectum and anal canal they form a thick layer, which in the 

 latter situation is known as the sphincter ani intemus. 



The submucous coat is in all respects similar to that of the small 

 intestine. 



The mucous coat is pale and greyish in colour, except in the 

 rectum, where it is red. Its epithelium is similar to that of the 

 small intestine. It is destitute of valvulae conniventes and villi, 

 and consequently presents a smooth surface. It contains large 

 numbers of the cr\'pts or follicles of Lieberkiihn, which abound in 

 mucus-secreting goblet cells. It also contains solitary glands or 

 lymphoid nodules, which are especially prevalent in the vermiform 

 appendix and caecum. The deepest part of the mucous coat is 

 formed by the muscularis mucoscB {muscularis interna). 



Blood-supply — Arteries. — These are as follows : (i) appendicular, 

 for the vermiform appendix ; (2) anterior and posterior caecal, for 

 the caecmn : (3) colic of ileo- colic, and right colic, for the ascending 

 colon ; (4) middle colic, for the transverse colon (all branches of the 

 superior mesenteric) ; (5) left colic, for the descending colon ; and 

 (6) sigmoid arteries, for the iliac colon and pelvic colon (the latter 

 two being branches of the inferior mesenteric). 



Veins. — ^The destination of the venous blood of the vermiform 

 appendix, caecum, ascending colon, and transverse colon is the 

 superior mesenteric vein, whilst the blood of the descending colon, 

 iliac colon, and pelvic colon is carried into the inferior mesenteric 

 vein. In both cases the further destination of the blood is the vena 

 portae. As in the small intestine, the veins have valves which are 

 competent in early life, but not so in the adult. 



The lymphatics will be found described on pp. 729 and 



730- 



Nerves. — These are derived from the superior mesenteric sympa- 

 thetic plexus, and the inferior mesenteric plexus, which latter 

 is an offshoot from the aortic plexus. The disposition of the nerves 

 corresponds with that in the small intestine. 



The large intestine diminishes gradually in size from its com- 

 mencement to its termination. Its diameter varies in different 

 parts, the extremes being 2h inches and i inch. 



Characters of the Large Intestine — Peritoneal Coat. — This presents at fre- 

 quent intervals small projections called appendices epiploicae. Muscular Coat. 

 — The longitudinal fibres are for the most part arranged in three taeniae. Mucous 

 Coat. — This is destitute of (a) valvulae conniventes, (b) villi, (c) Brunner's 

 glands, and (d) Peyer's patches, but it is provided with (i) Lieberkuhn's 

 crypts, and (2) solitary glands or lymphoid nodules. Outline of Tube. — 

 The bowel presents three rows of sacculi, except in the vermiform appendix 

 and rectum. 



