512 



SPECIAL PHYSIOLOGY. 



cava, and the aorta, and passing slightly upwards, joins the jejunum, 

 opposite a line corresponding with the superior mesenteric artery and 

 vein. In the concavity of the curve of the duodenum, is placed the 



Fig. 90. 



Fig. 90. Portion of the small intestine, dissected, to show the position of its several coats, s, the 

 outer, smooth, serous, or peritoneal coat, m, the muscular coat, composed of an outer layer of longitudinal 

 fibre?, and an inner layer of circular fibres, c, the submuoous and mucous coats united together. Much 

 reduced in size. 



right end or head of the pancreas, which is here attached to the in- 

 testine. The common bile duct and the pancreatic duct, open into the 

 duodenum. 



The jejunum, j, forms about two-fifths, and the ileum, i, i, the re- 

 maining three-fifths of the part of the small intestine below the duo- 

 denum. The jejunum occupies the middle and left regions of the 

 abdomen ; whilst the ileum is placed in the middle, lower, and right 

 regions, and, occasionally, partly descends into the pelvis. The termi- 

 nation of the ileum in the large intestine, c, is situated in the right 

 iliac fossa. The jejunum has thicker and dark-colored coats, and is 

 somewhat wider than the ileum, the average diameter of the former 

 being 1J inch, that of the latter 1 inch. 



Fig. 91. 



Fig. 91. Portion of the small intestine, laid open to show the smooth internal coat or mucous membrane, 

 which is here thrown into numerous transverse double folds or ridges, which are permanent. These are 

 the valvulae conniventes. v. A patch of the so called Peyer's glands, or glandular Bgmiuatee, or aggregate, 

 with its little component round sacs, is shown at p. The oblong white piece of card, partly covering the 

 patch of Peyer, and marked with an asterisk, *. shows the relative size of the piece of mucous membrane 

 represented in Fig. 08. 



The membranous walls of the small intestine are composed, like those 

 of the stomach, of four coats; viz., the serous, muscular, areolar, and 

 mucous coats. The serous coat, Fig. 90, , derived from the perito- 



