THE C^CUM. 1667 



meso- appendix, is in its conventional form described as having four sides : a superior 

 on the ileum, a right one on the caecum, an inferior joining the appendix or the 

 meso-appendix, and a free concave one looking towards the left and overhanging 

 the entrance to the fossa, which may be nearly 4 cm. {i}4 in. j in depth. The fold 

 usually contains only small vessels, and has been described as "bloodless." It 

 sometimes contains muscle-fibres passing between the ileum and caecum. The size 

 as well as the formation of this pocket is very variable. When we consider the 

 extreme variability of the meso-appendix which is concerned in its typical forma- 

 tion, it is manifest that such must be the case. Sometimes the meso-appendix is in 

 no way connected with it, only a small fold of peritoneum passing from the ileum to 

 the caecum at the side most removed from the mesentery. Berry found this fossa in 

 74 per cent! 



The Retro-Colic Fossa. — In the great majority of cases the posterior sur- 

 face of the caecum lies free in the abdominal cavity, covered by its original peri- 

 toneum. At a variable distance from it the back of the colon becomes adherent to 

 the posterior abdominal wall and to the front of the right kidney ; hence there is, 

 or may be, especially if the colon be drawn away from the wall, a fold on either side 

 stretching from the gut to the wall. These are the ligaments of the colon, the exter- 

 nal and the interyial. The former runs outward and downward from the side of the 

 colon along the abdominal wall, or perhaps across the lower end of the kidney, and 

 presents a free concave border overhanging a pouch running upward and outward. 

 The internal or mesian fold is the more often distinct, and is formed chiefly by the 

 insertion of the mesentery. According to its degree of development, the free falci- 

 form edge overhangs a pouch, looking downward and more or less to the right. 

 The fold may be continued downward either to the right or to the left. In the 

 former case it may form a pocket, of which the lower end opens upward. It is 

 clear therefore, that with both these folds well developed a retro-colic fossa exists, 

 which is shown when the caecum is turned up. Its greatest depth is in the middle 

 behind the colon, and it is continued downward on either side under the folds 

 caused by these ligaments. Should either ligament be wanting, there can be no 

 fold on that side. Some authors have thought it best to describe an external and 

 an internal fossa under each of the ligaments, of which the internal is the more fre- 

 quent ; it is more simple, however, to describe only one. The fossa may be sub- 

 divided by a median fold. Very often there is no definite fossa at all. The internal 

 part is more commonly well developed than the external. 



The subcaecal fossa is an uncommon pouch, sometimes small and sometimes 

 large, situated above the middle of the iliac fossa. It seems to be due to an irregu- 

 lar development of the iliac fascia, which forms a pocket in itself, with the mouth 

 above, guarded in front by a semilunar fold. The fossa is lined by the parietal peri- 

 toneum. It may unite with the inner fold of the retro-colic fossa, or the two may 

 exist at the same time. It may contain the appendix, even a part of the caecum, 

 or, according to Jonnesco, coils of the small intestine. 



Blood-Vessels. — The artery supplying the caecum is the ileo-colic, a branch 

 of the superior mesenteric artery, which sends to it both an anterior and a larger 

 posterior branch, which ramify downward over the front and back of the caecum. 

 A large branch from the posterior division runs between the folds of the posterior 

 retinaculum ; less constantly a smaller vessel courses in the anterior one. The 

 segments of the ileo-caecal valve are very vascular. The artery of the vermiform 

 appendix arises from the posterior division of the ileo-colic, crosses the back of the 

 ileum, and runs in the fold of peritoneum to the end of the appendix. The veins 

 of the caecum are arranged on much the same plan as the arteries. That of the 

 appendix is relatively more important, receiving tributaries from the front and the 

 back of the caecum. It passes behind the end of the ileum to the ileo-colic vein. 



The lymphatics are divided into a posterior and an anterior set. The former 

 empty into small nodes on the back of the caecum beneath its peritoneal covering. 

 The anterior ones are in or near the fold between the caecum and colon. The appendix 

 contains a large lymph-sinus at the base of the follicles. Lymphatics pass through 

 the interruptions of the muscular layer. They may enter a node in the peritoneal 

 fold in the angle between the caecum and ileum. There are several possible communi- 



