412 THE DIGESTIVE APPARATUS IN MAMMALIA. 



abdominal cavity. It is nevertheless fixed : 1, By its origin, to the caecum 

 and to the serous fraenum which attaches it to that receptacle ; 2, By the 

 adherence of its terminal portion to the pancreas and the cross of the caecum ; 

 3, By the mesocolon. The latter ligament forms, in the concavity of the 

 pelvic flexure a kind of racket, the handle of which is prolonged to a short 

 distance between the two branches of the colic flexure. Beyond this, these two 

 branches are directly placed side by side. 



External surface. We Imve seen that the large colon does not offer the 

 same diameter everywhere, and that it is bosselated, plicated, and traversed 

 by longitudinal bands ; it is, however, important to study in detail this dis- 

 position of its external surface in each of the regions already named. 



At its origin, the large colon is extremely narrow, and scarcely equal to 

 the small intestine. But it soon dilates and assumes a considerable volume, 

 which it preserves beyond the pelvic flexure. It then becomes progressively 

 constricted to the middle of its third portion, where the diameter, reduced to 

 its minimum, is yet much greater than at the origin of the first portion. 

 Near the diaphragmatic flexure, the large colon is again gradually dilated, 

 and finishes by acquiring, near its termination, the greatest volume it has 

 yet exhibited. The muscular bands which maintain its transverse folds 

 throughout the whole extent of its first dilated portion, are four in number. 

 Three disappear in arriving towards the pelvic curvature, and the only one 

 remaining is that which is placed in the concavity of that curvature. At 

 the second dilatation there are three bands, two of which are prolonged to the 

 floating colon. The transverse folds formed by these flat bands are but 

 faintly marked towards the pelvic curvature, and are altogether absent in 

 the narrow portion succeeding it ; it is only in the whole extent of the first 

 dilatation that they are deepest and most numerous. 



Internal surface. This is exactly like that of the caecum. 



Structure. The serous membrane envelops the whole organ, except in 

 those places where it comes in contact with itself or with other viscera. So 

 it happens that the peritoneum, in ' passing from the sublumbar region to 

 the last portion of the colon, does not cover the surface which adheres by 

 cellular tissue to the inferior aspect of the pancreas and caecum ; neither, in 

 being carried from one branch of the colic flexure to the other, does it envelop 

 their opposed sides, except at the pelvic flexure, where it forms the meso- 

 colon. 



The muscular tunic does not differ in its arrangement from that of the 

 caecum ; neither does the mucous membrane. The arteries emanate from the 

 great mesenteric ; they are the two colic arteries. The two satellite veins 

 soon form a single trunk, which enters the vena portae. The lymphatics empty 

 themselves into Pecquet's reservoir. The nerves emerge from the great 

 mesenteric plexus. 



THE SMALL, OR FLOATING COLON (Fig. 204). This is a bosselated tube, 

 which succeeds the large colon, and is terminated in the pelvic cavity by the 

 rectum. 



Length Form Course Relations. This tube is about 10 feet in length, 

 and offers a disposition analogous to that of the small intestine, except that 

 it is double the size of that viscus, is regularly bosselated on its surface, and 

 is provided with two wide and thick longitudinal bands, one on the side of 

 its great, the other on its small, flexure. Arising from the terminal 

 extremity of the large colon, to the left of the caecum, where it responds to 

 the termination of the duodenum, and where it receives the insertion of the 

 great omentum, this intestine is lodged in the left flank, forming folds which 



