THE COLON. 1671 



thus found are due to a displacement of the peritoneum, which is but loosely attached. 

 True mesenteries are probably less frequent. 



At the sigmoid flexure the peritoneum usually begins to surround the gut, 

 although the point at which this commences may be much lower. In the former 

 case the line of origin of the mesentery descends tolerably straight to the middle of 

 the third sacral vertebra, where it ends. The gut may, however, be pretty closely 

 bound down to the iliac fossa as far as the true pelvis over the posterior border of 

 the obturator foramen, in which case the line of attachment runs thence backward 

 along the border of the true pelvis until it crosses the sacro-iliac joint, after which 

 it descends across the sacrum. There may, of course, be an indefinite number of 

 variations between these extremes. The attachment to the sacrum is usually near 

 the median line over the second and third vertebrae, but it may diverge to either 

 side of it. Variation also exists as to the point at which the mesentery ends. The 

 greatest breadth — i.e., from origin to insertion — of the latter is usually found in the 

 part which springs from the first sacral vertebra. It is, on the average, about 9 cm., 

 rarely less than 5, not more than 16 ; exceptionally it may be as much as 25 cm. 

 With a long loop it is, of course, relatively narrow at its origin. 



The intersigmoid fossa is an inconstant small peritoneal pouch, present 

 about three times out of four, on the under side of the mesentery of the sigmoid 

 flexure, which is shown by throwing the loop upward and to the right. It is ob- 

 viously due to the failure of the sigmoid mesentery to unite completely with the 

 peritoneum of the posterior wall, and consequently is under the edge of the part that 

 fails to unite, lying usually just above the true pelvis near the common iliac artery. 

 The orifice of the pocket is very likely to be circular, with a diameter of from 1-3 

 cm. , in most cases nearer the lower figure. The pouch may be quite rudimentary, 

 or may extend up like a tunnel between the layers of peritoneum for an inch or two, 

 or exceptionally for a greater distance. 



Development and Growth. — The length of the intestines, and especially of 

 the colon, is, according to Treves, singularly constant at birth. He found the 

 average length of the small intestine about 287. cm. (9 ft. 5 in. ) and that of the large 

 about 56 cm. (i ft. loin. ). It is remarkable that while during the first two months 

 the small intestine grows at the rate of about two feet a month, the large intestine 

 remains of the same length for three or even four months. This is due to the fact 

 that during this period the large intestine grows at the expense of the sigmoid flexure, 

 which at birth forms nearly one-half of the whole, while at four months it has 

 assumed approximately its permanent proportions (Treves). After this the growth of 

 both small and large intestine is extremely irregular, as shown by the following table : 



Observer. 



Dwight. 



Dwight. 



Treves. 



Dwight. 



Treves. 



Treves. 



As the sigmoid flexure is relatively large in the infant and the pelvis very small, 

 the convexity of the loop lies in the right side of the abdomen. 



Variations. — The mesentery of the small intestine and of the ascending and the transverse 

 colon may remain attached only at the origin of the superior mesenteric artery, giving the con- 

 dition known as inesenterium cominujte. The ascending colon may, on the other hand, be so 

 long as to make secondary folds. Curschmann ' has seen its mesentery long enough to be 

 twisted. The transverse colon may be short, wanting one or both flexures. In the latter case 

 the ascending and the descending colon are almost like the sides of an inverted V. Probably 

 much more often the transverse portion may be too long and descend in the middle like an M, 

 with the middle point at the pelvis. A fold is more common at the left than the right. A 

 double fold of the transverse colon has been seen. This part of the gut, when over large, may 

 decidedly diminish the area of the liver dulness. The descending colon may also present 

 folds, but an immense sigmoid flexure, which usually is accompanied by great length of the 

 large intestine, is more common. The convexity of this fold may reach to the transverse 

 colon or to the caecum. Sometimes the sigmoid flexure consists of two successive folds. 



* Deutsches Archiv fiir Klin. Med., Bd. liii., 1894. 



