THE INTESTINES 257 



^. The rectum. As soon as the colon has reached the 

 basis of the sacrum, it ends, and it then assumes the 

 name of rectum, being to a certain extent straight ; 

 however, it is not perfectly so, as it follows the 

 curve of the bones. It terminates by a large ex- 

 tremity, called the anus. The rectum will hold 

 about three gallons of water or fluid matter. The 

 outer extremity is furnished with a circular muscle, 

 called the sphincter ani, the use of which is to keep 

 the anus closed, to retain the feculent matter until 

 so much of it be accumulated in the rectum as to 

 excite a desire to discharge it. 



PLATE IX, Fig. i. 



This figure Is intended to display the relative 

 situations of the principal organs, with only part of 

 the intestinal canal. These lie exteriorly to other 

 important viscera. 



a, a, a. The different lobes of the lungs, already described, page 

 230. Its vessels are seen upon its surface. 



b. The pericardium, or bag which surrounds the heart. 



c. The heart. 



a^ a, d. The colon, already described in Plate vin, fig. 5, a, a^ a, a. 



e. The ligamentous bands of the colon, which pucker it 

 into folds. 



/,/,/,/. The ribs. 



g. The sternum or breast-bone, removed from its junction 

 with the ribs, and thrown back to exhibit the contents 

 of the chest beneath. 



h. The diaphragm, already described, page 241. 



/, z", 2, i. The skin thrown back, to show the contents of the chest. 



j. One of the small intestines. 



k. The ensiform, or sabre-shaped cartilage. 



/, /, /. The neck. 



ni. The situation of the trachea, or windpipe. 



