THE ABDOMEN 697 



communicates with the caecum is occasionally guarded by a fold of 

 mucous membrane, which is known as the valve of Gerlach. The 

 appendix is provided with a mesentery, caJled the appendicular 

 mesentery or meso- appendix. It seldom reaches more than half 

 or two-thirds along the appendix, which latter is thus rendered 

 more or less convoluted or serpentine. The meso-appendix and its 

 variations will be found described on p. 725. 



The position occupied by the appendix is extremely variable. According 

 to Lockwood and RoUeston, the normal positions may be tabulated as 

 follows : 



1. The vermiform appendix often lies under the left or iaferior layer of 

 the mesentery, where it takes a course upwards and to the left in the direction 

 of the spleen. (According to Treves this is its usual position.) 



2. It may lie on the brim of the pelvis, or it may project into the pelvic 

 cavitv. 



3. If the appendicular mesentery is long, the appendix may lie to the right 

 of the caecum and ascending colon, in which situation it may ascend over the 

 right kidney towards the right lobe of the liver. 



4. It may lie free over the caecum and ascending colon. 



5. It may he free underneath the caecum. (This is the second most common 

 situation according to Treves.) 



As regards abnormal positions of the vermiform appendix, it may, amongst 

 other situations, be found lying in the retro-caecal, or in the ileo-caecal, fossa. 

 It has been found extending horizontally across the vertebral column at the 

 level of the lumbo-sacral angle, with its tip resting on the left psoas magnus 

 muscle (Treves). 



Ascending or Right Colon. — ^This extends from the caecum, on a 

 level with the ileo-caecal orifice, to the under surface of the right 

 lobe of the liver at a point to the right of the gall-bladder. Here 

 it describes a bend, called the hepatic flexure, which indents the 

 liver, and so gives rise to the impressio colica. The ascending 

 colon occupies a part of the right iliac, right lumbar, and right 

 hypochondriac regions, in which it lies deeply, being in contact 

 with the posterior abdominal wall. Posteriorly it rests upon a 

 portion of the right iliacus muscle covered by the fascia iliaca, the 

 right quadratus lumborum invested by its sheath, and the front 

 of the right kidney in its lower and outer part. Anteriorly it is 

 more or less covered by the coils of the jejunum and ileum. 

 Internally, it has the coils of the jejunum and ileum, and the right 

 psoas magnus muscle, covered by its fascia. The ascending colon 

 in most cases is covered by peritoneum in front and at the sides, 

 but not behind. Sometimes, however, it is completely invested by 

 the serous membrane, which then forms behind it a mesentery, 

 called the ascending meso-colon. Occasionally a peritoneal fold is 

 met with, which extends from the right side of the ascending colon 

 to the abdominal wall at, or a little above, the -level of the iliac 

 crest. It is called the sustentaculum hepatis, and occurs in about 

 18 per cent, of cases (Treves). It presents anteriorly a free con- 

 cave border, and it measures about i^ inches in width, and about 

 2 inches from before backwards. 



Hepatic Flexure. — ^This is the bend formed by the gut between 



