286 AN ELEMENTARY TEXT-BOOK OF BIOLOGY. 



pierces the diaphragm, and enters the stomach, a large trans- 

 versely placed sac, with firm thick walls. 



Its left (cardiac) portion is much dilated, while its right (pyloric) portion 

 is thickened. Posteriorly it presents a convex margin, the greater curva- 

 ture, and anteriorly a concave margin, the lesser curvature, to the left of 

 which is the cardia, or opening of the gullet. The pylorus where the 

 duodenum commences, is at the extreme right of the pyloric end. The 

 mucous membrane lining the stomach is raised into irregular longitudinal 

 ridges, or rugce. Between stomach and duodenum there is an inwardly 

 projecting rim, the pyloric valve. 



The stomach is succeeded by a much convoluted intestine, some 

 15 or 16 times the length of the body, and divided into small 

 and large. The first part of the thin-walled small intestine,* 

 the duodenum, forms a longitudinally directed U-shaped loop 

 nearly the length of the abdominal cavity. It passes insensibly 

 into the much longer ileujti, in the wall of which there are oval 

 thickenings, Peyer's patches, here and there. 



This part of the intestine finally opens into the crecum (see below], and 

 at this point its wall is much thickened to form the sacculus rotundus* 

 The mucous membrane of the small intestine is raised into numerous 

 irregular transverse ridges, the valvulce connivences, from which project an 

 immense number of villi. 



The large intestine is divided into caecum, colon, and rectum. 

 The caecum is a very large thin-walled sac, nearly 2 feet in length, 

 interposed between the ileum and colon. Its wall is marked 

 externally by a spiral groove. One end, near which the ileum 

 opens, is continuous with the colon, while the other terminates- 

 blindly in a thick-walled finger-like vermiform appendix. 



A spiral fold, corresponding to the external groove, projects into the 

 cavity of the caecum, with which cavity the sacculus rotundus com- 

 municates by a small rounded aperture (ileo-colic valve), and which opens, 

 by a larger aperture into the colon. The lining mucous membrane is raised 

 into minute elevations ; in other words, is papillose. 



The colon is a moderate-sized thin-walled tube with baggy 

 walls, along which three smooth longitudinal bands run. It 

 passes insensibly into the narrow rectum, which, after some con- 

 volutions, runs back within the pelvic cavity, below the backbone, 

 and above the urinogenital organs, to the anus. The mucous 

 membrane lining the colon is papillose, that lining the rectum 



* In human anatomy this is divided, somewhat arbitrarily, into three 

 parts duodenum, jejunum, and ileum. The two last are here included in* 

 the term " ileum." 



