1172 



DIGESTIVE SYSTEM 



4. In the fourth type, the development 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 caecum. The root of the 

 appendix is posterior to that angle. There is no trace of the original apex, and the appendix 

 appears to spring almost from the ileo-csecal junction (fig. 933, D.) 



The ileo-caecal valve. — The ileo-csecal valve [valvula coli] is situated at the 

 entrance of the ileum into the large intestine at the upper border of the caecum, 

 on the posterior aspect and toward the medial side (fig. 932). The valve usually 

 lies nearly opposite the middle of a hne from the anterior superior iliac spine (left) 

 to the umbilicus. The ileum passes from below upward and toward the right, and 

 terminates with a considerable degree of obliquity. The valve is formed by two 

 lip-like folds projecting into the large intestine, the upper [labium superius], 

 and the lower [labium inferius]. They are a little oblique. The opening between 

 them takes the form of a narrow transverse slit about 1.2 cm. in length. At the 

 ends of the slit the valves unite and are prolonged at either end as a ridge [frenu- 

 lum valvule coli] partially surrounding the intestine. 



Villi cover that surface of the folds looking toward the ileum; the surface toward the large 

 intestine is free from villi. In the formation of this valve the longitudinal muscular fibres 

 pass across from the ileum to the large intestine without dipping down between the two layers 

 of each fold. The circular muscular fibres, on the other hand, are contained between the 

 mucous and submucous layers which form these folds. 



The efficiency of the valve in preventing the return of faeces is due largely to its oblique 

 position. (Symington.) 



Fig. 934.- 



-C^cuM, Vermiform Process, and End of Ileum, with the Blood -supply and 

 THE Neighbouring Foss^. (Woolsey, after Merkel.) 



Ileo-colic A. 



Sup. ileo-caec. fossa 



Course of appendic. a. 

 behind ileum 



Plic. ileocaec. ant. 



nf. ileo-caec. fossa 

 Mesenteriolum 



Appendic. a. 



Subcsecal fossa 



Ileo-caecal fossae. — About the caecum, and especially in the vicinity of the ileo- 

 cecal junction, are certain fossae collectively known as the ileo-caecal fossae. Two 

 only appear to be fairly constant, although a third is now and then present. 



The first, the superior ileo-coecal or ileo-colic fossa, is formed by the passage across the 

 junction of the caecum and ileum of the anterior caccal artery, a branch of the ileo-colic artery, 

 which produces a fold of peritoneum [plica ileocolica] limiting a pouch. It is on the anterior 

 aspect of the ileo-colic junction, and the pouch opens downward (figs. 906, 934). It is present 

 in about one-third of all cases. 



The second fossa is not quite so simple. If the caecum be turned upward so as to expose 

 its posterior surface as it lies in situ, and if the appendix be drawn down so as to put its mesentery 

 on the stretch, a peculiar fold will bo found to join that mesentery (fig. 934). This fold arises 

 from the border of the ileum opposite the insertion of its mesentery. It then passes over the 

 ileo-caecal junction on its inferior aspect, is adherent to the ca;cura, and finally joins the surface 

 of the mesentery of the appendix. This fold is peculiar in the absence of any visible vessels, 

 and is often known as the 'l)loodloss fold of Treves.' Between it and the appendix there is an 

 almost constant fos.sa, the inferior ilro-arcal fossa. It is usually large, admitting two fingers, 

 and occurs in nearly Sf) per cent, of all cascK. It is bounded on one side by the small intestine, 

 and on the other by Ihc (•;i'(;uiii. The a])i)nndix is occasionally foimd in the fossa. 



The suhcncal or rcirorolic fossa is behind the ca>cura and is found in about ten per cent, of 

 all cases. It may extend for some distance behind the ascending colon. The appendix may be 

 lodged in this fos.sa. 



ParaccEcal fo.ssie rarely occur, at the side of the c;ecum. 



Variations. — In addition to variations already mentioned the caecum may vary in its general 



