510 



MUCOUS COAT. 



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 direction. 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 circular 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 the upper part of the ileum, it forms 

 valvular folds called valvulceconniventes, 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 extend 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 



Fig. 223.* 



intestine as compared with the jejunum and duodenum. At the termina- 

 tion of the ileum in the caecum, the mucous membrane forms two folds, 

 which are strengthened by the muscular coat, and project into the caecum. 

 These are the ileo-c&cal valve (valvula Bauhini). In the caBcum and colon 

 the mucous membrane is raised into crescentic folds, which correspond 



* A vertical section of the anterior parietes of the anus, with the whole canal dis- 

 played so as to show the relations of the sacculi of the middle region, and their relations 

 to the surrounding parts, their orifices being marked with bristles. 1, 1. Columns of the 

 rectuin. 2, 2. Rudiments of columns. 3. Internal sphincter. 4. External sphincter. 

 6. Rudimentary or imperfect sacculi. 5, 5. Radiated folds of the skin, terminating on 

 **'e surface of the nates. 7. A bristle in one of the sacs. G. 



