482 TEE DIGESTIVE APPARATUS IN MAMMALIA 



it rests on the xiphoid cartilage of the sternum (Fig. 282, g). Here begins the 

 second portion of the viscus, which is in immediate contact with the inferior 

 abdominal wall, and extends backwards into the pelvic cavity, where it is 

 inflected to the left to constitute the sigmoid or pelvic flexure. This curvature — 

 the centre of the colic loop — is in relation with the rectum and bladder, as well 

 as with the deferent canals, or the uterus and ovaries, according to the sex. It is 

 succeeded by the third portion of the colon, which is carried forward, above, and 

 to the left of the preceding. Bound to the second division by peritoneum and con- 

 nective tissue, this new section reaches the tendinous centre of the diaphragm, and 

 is then doubled upwards and to the right. The flexure arising from this third 

 duplicature is called the diaphragmatic, because of its relations with the musculo- 

 aponeurotic membrane that partitions the great cavity of the trunk, or the gastro- 

 hepatic curvature, in consequence of its lying equally 

 Fig. 285. against the liver and stomach (it is also designated the 



sigmoid flexure) (Fig. 282, k). To this flexure succeeds 

 the fourth and last portion of the large colon, bound to 

 the first portion, as the second is to the third. This 

 extends, posteriorly, to the base of the caecum, where it 

 terminates in a sudden contraction, and is continued by 

 the small colon ; it occupies the sublumbar region, and, 

 through the medium of connective tissue, is applied 

 against the inferior face of the pancreas and the inner 

 PLAN OF THK COLON. sldc of thc csjcal arch.' 



Mode of attachment. — The lai'ge colon can be easily 

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

 the caecum and to the serous frsenum which attaches it to that receptacle. 2. 

 By the adherence of its terminal portion to the pancreas and arch of the caecum. 

 3. By the meso-colon. 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 have seen that the large colon does not offer the same 

 diameter everywhere, and that it is sacculated, plicated, and traversed by longi- 

 tudinal bands ; it is, however, important to study in detail this disposition 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, it 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, 



* We have, in some instiinces, found the large colon doubled on itself in an inverse sense — 

 the second and third portions being placed above and in front of the first and fourth, with the 

 pelvic flixure touching the sublumbar region, in front of the caecum, and the point of the latter 

 directed back towards the pelvis. 



