THE KIDNEYS 1379 



small proportion (1.8 per cent., however, does the true primitive type of ascending mesocolon 

 persist, continuous with the mesentery of the small intestine (G. M. Smith). Such an anomaly 

 renders the patient liable to volvulus of the ileo-csecal region. In the common types of in- 

 complete fusion of its peritoneal attachments the colon is inadequately adapted to the upright 

 position and is predisposed to ptosis. A layer of peritoneum sometimes found passing down- 

 ward and medially from the parietes in the right flank onto the front of the ascending colon, 

 known as Jackson's pericolic membrane, is probably due to persistence of an early stage in the 

 development of the great omentum, which passes to the right across the ascending colon to 

 join with the parietal peritoneum before the descent of the ctecum is complete, and so is the most 

 primitive agent in fixing the proximal colon back in the right loin. This membrane is usually 

 associated with a congenitallv mobile ascending colon (Morley).* 



At the hepatic flexure the colon bends forward and to the left, leaving the front of the kidney 

 to which it is fixed, and crossing the second part of the duodenum. In the region of the flexure 

 three inconstant peritoneal folds are met with giving it additional attachment to the neigh- 

 bouring parts, viz., (1) the phreno-colic and less commonly (2) the hepato-colic and (3) cysto- 

 colic ligaments (Testut). They must not be confused with pathological adhesions acquired 

 after birth. 



The transverse colon is freely mobile except at its extremities. It crosses the 

 abdomen with a convexity downward and forward, being separated from the 

 anterior abdominal wall in the middle region by the great omentum. 



At the mid-line it usually lies near the umbilical plane in the recumbent posture, consider- 

 ably lower in the erect, but may be found anywhere from the infra-costal plane to the pubes, 

 depending on the tonicity of the stomach. Its main artery, the middle colic branch of the 

 superior mesenteric, must be avoided carefully in the operations of gastro-enterostomy and gas- 

 trectomy, since ligature of it causes gangrene of the transverse colon. 



The splenic flexure lies far back in the left hypochondrium and is considerably 

 higher than the hepatic flexure. It is in contact with the lower end of the spleen, 

 and is almost invariably held firmly in position by its phreno-colic ligament, 

 derived from the left extremity of the great omentum. 



The descending colon is of narrower calibre than the preceding parts and 

 usually is found firmly contracted and empty. It passes downward and forward 

 in the angle between the psoas and quadratus lumborum and obliquely across 

 to the right the iliac fossa to end in the sigmoid or pelvic colon. The lower part 

 of the descending colon, from the iliac crest to the pelvic brim, is often termed 

 the iliac colon. 



In its upper part it lies in front of the convex lateral margin of the left kidney. The varia- 

 tions in its peritoneal attachments have been referred to above (p. 1242). The operation of 

 lumbar colostomy, common in pre-antiseptic days, was performed through an incision in the 

 back parallel with the last rib. The colon lies 2.5 cm. (1 in.) to the lateral side of the edge of 

 the sacro-spinalis, between the twelfth rib and ihac crest. The occurrence of a mesocolon here 

 was a common source of difficulty in gaining access to the bowel without opening the peritoneum. 



The pelvic colon (also known as the sigmoid or omega loop (Treves), is almost 

 as long as the transverse colon, and forms a loop, the two ends of which, at the 

 pelvic brim and at the front of the third sacral vertebra respectively, are placed 

 somewhat closely together. The loop is thus anatomically predisposed to axial 

 rotation, and is the commonest seat of volvulus in the whole intestinal tract. 



On the left and inferior aspect of the pelvic mesocolon near its base, a small peritoneal 

 fossa {inter sigmoid) is usually found in the angle formed by the root of the mesocolon and 

 the parietal peritoneum. It occasionally contains an internal hernia which may become 

 strangulated. 



The upper part of the pelvic colon is frequently brought out and opened through an inci- 

 sion in the left iliac region to form an artificial anus in cases of inoperable growth of the 

 rectum. 



In advanced life, and in the clu'onically constipated, certain diverticula of mucous membrane 

 are occasionally met with which project through the vascular gaps of the muscular coat into 

 the bases of the appendices epiploicse in this region, and also between the layers of the pelvic 

 inesocolon. They often contain fsecal concretions and may become inflamed or even perforate, 

 forming an abscess in the left iliac fossa, t 



The junction of pelvic colon and rectum opposite the third sacral vertebra forms a more or 

 less acute angle and constitutes the narrowest part of the colon. It is a frequent site of stricture. 



The kidneys. — These lie at the back of the abdominal cavity so deeply in the 

 hypochondriac and epigastric region as to be beyond palpation in most individuals, 

 unless enlarged or unduly mobile. The lower end of the right being slightly 

 lower than its fellow, encroaches in health upon the lumbar and umbilical 

 regions, and may be palpable on deep inspiration in spare subjects. These 



* Lancet. Dec, 1913. 

 jt McGrath: Surgery, Gynecology and Obstetrics, vol. 15, 1912, 429. 



