MUCOUS MEMBRANE OF STOMACH. 505 



vascular at the great extremity, and becomes thicker and lighter in 

 Colour towards the pyloric extremity. It is. formed into plaits or 

 rugce, which are disposed for the most part in a longitudinal direc- 

 tion. The rugae are most numerous towards the lesser end of the 

 stomach ; while around the cardiac orifice they assume a radiated 

 arrangement. At the pylorus the mucous membrane forms a cir- 

 cular or spiral fold which constitutes a part of the apparatus of the 

 pyloric valve. In the lower half of the duodenum, the whole length 

 of the jejunum, and in the upper part of the ileum, it forms valvular 

 folds called valvulce. connivent.es, which are several lines in breadth 

 in the lower part of the duodenum and upper portion of the jejunum, 

 and diminish gradually in size towards each extremity. These 

 folds do not entirely surround the cylinder of the intestine, but ex- 

 tend for about one half or three-fourths of its circumference. In the 

 lower half of the' ileum the mucous lining is without folds ; hence 

 the thinness of the coats of this intestine as compared with the jeju- 

 num and duodenum. At the termination of the ileum in the cascum, 

 the mucous membrane forms two folds, which are strengthened by 

 the muscular coat, and project into the caecum. These are the ilio- 

 caical valve (Valvula Bauhini). In the csecum and colon the mucous 

 membrane is raised into crescentic folds, which correspond with the 

 sharp edges of the sacculi ; and, in the rectum, it forms three val- 

 vular folds,* one of which is situated near the commencement of the 

 intestine ; the second, extending from the side of the tube, is placed 

 opposite the middle of the sacrum ; and the third, which is the 

 largest and most constant, projects from the anterior wall of the 

 intestine opposite the base of the bladder. Besides these folds, the 

 membrane in the empty state of the intestine is thrown into longitu- 

 dinal plaits, somewhat similar to those of the cesophagus; these 

 have been named the columns of the rectum.f 



Structure of Mucous Membrane. This membrane is analogous to 

 the cutaneous covering of the exterior of the body, and resembles 

 that tissue very closely in its structure. It is composed of three 

 layers, an epithelium, a proper mucous, and a fibrous layer. 



The Epithelium is the cuticle of the mucous membrane. Through- 

 out the pharynx and oasophagus it resembles the cuticle, both in 

 appearance and character. It is continuous with the cuticle of the 

 skin at the margin of the lips, and terminates by an irregular bor- 

 der at the cardiac orifice of the stomach. At. the opposite extre- 

 mity of the canal it terminates by a scalloped border just within the 

 verge of the anus. In the mouth it is composed of several laminae 

 of oval vesicles and ihin angular scales. Each vesicle and each 

 scale possesses a central nucleus, and within the nucleus is a minute 



* Mr. Houston, " On the Mucous Membrane of the Rectum." Dublin Hospital Re- 

 ports, vol. v. ^L 



t The spacesbetween the columns of the rectum become closed at the anus so as to 

 form a scries of pouches represented in the accompanying cut. These pouches are 

 sometimes dilated and produce a disease first described by Dr. Physick. (See Gibson's 

 Surgery.) The mucous membrane of the rectum is connected to the muscular coat 

 by a very loose cellular tissue as in the oesophagus. G. 



61 



