THE INTESTINES. 413 



are mixed with the convolutions of the small intestine. It afterwards 

 passes into the pelvic cavity, to be directly continued by the rectunx 



Mode of attachment. Floating like the small intestine, the small colon is 

 suspended by a serous layer, exactly similar to the mesentery proper, though 

 wider, and named the colic mesentery. This mesentery is detached from the 

 sublumbar region, not from around a central point, but from a line extending 

 from the great mesenteric artery to the bottom of the pelvic cavity. It is 

 narrower at its extremities than in its central portion. 



Interior. The internal surface of the floating colon shows valvular folds, 

 analogous to those of the caecum and large colon. It is in the intervals 

 between these that the faecal matters are moulded into balls. 



Structure. The serous membrane is without special interest, and the 

 muscular tunic is similar to that of the large colon. The mucous membrane 

 is also the same. These membranes receive their blood by the small, and 

 a branch of the great, mesenteric artery. A venous trunk, passing between 

 the layers of peritoneum composing the mesentery, carries back the blood 

 to the vena portae. The lymphatics are nearly as fine and as numerous as 

 those of the small intestine ; they enter the same confluent, the reservoir of 

 Pecquet. 



FUNCTIONS OP THE COLON. In this intestine is accomplished the ab- 

 sorption of fluids, and of soluble alible matters. When the alimentary mass 

 arrives in the small colon, deprived of its assimilable principles and 

 charged with excretory substances thrown out on the surface of the intes- 

 tinal tube, it loses its name and receives that of excrement or fceces. These 

 excrements, compressed by the peristaltic contractions of the muscular tunic, 

 are divided into little rounded or oval masses, which find their way to the 

 rectum, where they accumulate, and whence, in due course, they are expelled. 



C. Rectum. (Fig. 204.) 



The rectum extends, in a straight line, from the entrance to the pelvic 

 cavity to the posterior opening of the digestive canal, or anus. It is no- 

 thing more, properly speaking, than the extremity of the small colon, the 

 limit which separates them being somewhat arbitrary ; it differs from that 

 viscus, however, in having no ridges, and in its walls being thicker and more 

 dilatable, so that it can be distended into an elongated pouch, and form a 

 reservoir or receptacle for the excrementitious matters until they are expelled. 



Relations. It responds, superiorly, to the roof formed by the os sacrum ; 

 inferiorly, to the bladder, the deferent canals, vesiculae seminales, prostate 

 gland, Cowper's glands, or to the vagina and uterus ; laterally, to the sides 

 of the pelvis. 



Mode of attachment. There ought to be considered 'as such: 1, The 

 posterior extremity of the colic mesentery, representing the mesorectum ; 

 2, An orbicular fold, constituted by the peritoneum in its circular reflection 

 around this viscera at the extremity of the pelvic cavity ; 3, The suspensory 

 ligaments of the penis, which, joining under the rectum, form a ring en- 

 circling the posterior extremity of the intestine (see Fig. 204 and the 

 description of the penis) ; 4, A thick, triangular fasciculus, comprising two 

 lateral parts, and composed of white muscular fibres ; this fasciculus, which 

 is really a prolongation of the muscular tunic of the viscera, is detached from 

 the rectum above the anus, and is attached to the inferior aspect of the 

 coccygeal bones, between the inferior sacro-coccygeal muscles, where its 

 outline can be seen beneath the skin when the tail is elevated. 



