TllK LARdE ISTESTINE <)71 



anterior band grows out of proportion to that part to tlie left of tin* band. Tlie 

 anterior wall becomes more devi'lopecl than the j)osterior, so that the ajjex is turned 

 so mu(!h to the left and posteriorly that it nearly meets tbe ileo-eseeal junction. A 

 false aj>ex is formed by the hiiihly developed ])art to the right of the anterior band. 

 This is the usual can-um foimd (iig. o75, C. ). 



4. In the fourth ty))e, the develojtment of the part to the right of the anterior 

 band is excessive, while the segment to the left of the band has atrophied. In this 

 form the anterior band runs to the inferior angle of junction of the ileum with the 

 cjecum. The root of the appendix is jjosterior to that angle. There is no trace of 

 the original apex, and the api)cndix a])pears to spring almost from the ileo-ca'cal 

 junction (fig. 575, D. ). 



()ll)cr variations. — The ca'cum may vary in its general development. It is some- 

 times small and insignificant, in other cases it reaches a large size. It may be so 

 rotated that the ileum })asses behind the colon and o))ens on the right side. The 

 posterior part has been seen much more develo])ed than the anterior, so that the 

 ileum has entered from the front, and the appendix has come off from the anterior 

 wall. The ca3cum may remain undescended, and be found just under the liver or 

 in the vicinity of the umbilicus. The ca3cum and colon may be suspended by a 

 mesentery common to the whole intestinal canal. In such cases the primitive 

 condition of the peritoneal fold which supports the small and large intestine is 

 permanently retained (page 997). 



The vermiform appendix. — Attached to what is really the original ajx'x of 

 the ca'cum is a narrow, blind tube: this is the vermiform appendix. It usually 

 comes off close to tlie ileo-ctecal valve on the inner and posterior side of the bowel, 

 though occasionally it forms the true apex of the caecum. In the adult the average 

 length is four inches, the extremes being one inch and six inches. In the majority 

 of instances the appendix is much twisted upon itself. Its usual position is ])ehind 

 the end of the ileum and its mesentery, and pointing in the direction of the sjaleen. 

 It may occasionally ascend vertically behind the caecum. 



It has a definite mesentery, which comes off from the left layer of the mesentery 

 of the ileum. Its origin from this layer is along a straight line which is situated 

 at a short distance from tlie intestine, and which is not (piite parallel with the 

 margin of the liowel. In general outline the mesentery is triangular. In theadidt it 

 does not extend along the whole length of the tube. It is, in fact, too short for the 

 appendix, and it is this that accounts for the twisted condition of the little process. 

 Along the free margin of the mesentery runs a branch of the ileo-colic artery. 



Ileo-caecal fossa. — About the ccecum, and especially in the vicinity of the ileo- 

 cecal junction, are certain fossse collectively knoAvn as the ileo-ca?cal. Two only 

 appear to be fairly constant. The first, tlie svperior ileo-caecal, is formed by the 

 passage across the junction of the caecum and ileum of a l)ranch of the ileo-colic 

 artery, which produces a fold of peritoneum limiting a pouch. It is on the anterior 

 aspect of the bowel, and the pouch o])ens downwards. 



The second fossa is not (juite so simple. If the ca'Cum l>e tinnied u]nvards so 

 as to expose its posterior surface as it WoBinsitu, and if the a]ipendix be drawn down 

 so as to put its mesentery on the stretch, a peculiar fold will be found t() join that 

 mesentery. This fold arises from that border of the ileum which is most remote 

 from the insertion of its mesentery. It then passes over the ileo-ca?cal junction on 

 its inferior aspect, is adherent to the caecum, and finally joins the surface of tlie 

 mesentery of the apjiendix. This fold is peculiar in tlie absence of any visible 

 vessels. Between it and the appendix there is an almost constant fossa, the inferior 

 ileo-aecal. It is large, admitting two fingers. It o]iens outwards, and is bounded 

 on one side by the small intestine, and on the other by the caxnim. 



The ileo-caecal valve. — The ileo-ca'cal valve, which is situated at the entrance 

 of the ileum into the large intestine at the u])per border of the ca'Cum, is found on 

 the inner side and towards the j)os-terior asjiect of the intestine. The ileum ])asses 

 from Vielow ujiwards and towards the right, and terminates with a consideralde 

 degree of obliquity. The valve is formed by two semilunar folds projecting into 

 the large intestine, the upper being nearly transverse, the lower being a little 

 oblique. The ojiening between them takes the form of a narrow slit about half an 

 inch in length, rounded in front but narrow behind. At the ends of the slit tlie 



