1034 



THE ORGANS OF DIGESTION. 



coalesce and are prolonged intofrcena or retinacula of the valve. The segments 

 are made by an invagination of parts of the wall of the ileum into those of the 



FIG. 653. Caecum and vermiform appendix. (Sap- 

 pey.) 1. Ileum. 2. Orifice of valve. 3. Inf. segment. 

 4. sup. segment. 5. Long muscular fibres from ileum. 

 6. Cul-de-sac of caecum. 7. Appendix. 8. Post, taenia. 

 9. Int. taenia. 10. Ant. taenia. 11. Sacculus. 



FIG. 654. Ileo-caecal valve. fSappey.) 1. Edge of 

 caecum. 2. Orifice of valve. 3. Inf. segment. 4. Sup. 

 segment: 5 and 6. Fraena. 7. Appendix. 8. Its mouth. 

 9. Semilunar fold. 10. Post, taenia. 11, 12, 12. Ant. 

 taenia. 13. Int. taenia. 



colon (Fig. 655). 



Each segment of the valve consists of two layers of mucous 

 membrane continued around the free border, 

 one from the small intestine and one from the 

 large, including between them submucosa and 

 circular muscular fibres ; the longitudinal fibres 

 and peritoneum are continued uninterruptedly 

 across from one intestine to the other and do 

 not enter their composition. If these two coats 

 be incised and traction made on the ileum, these 

 valves can be unfolded and drawn out of the 

 colon, the ileum appearing to open into the 

 intestine by a large funnel-shaped orifice. The 

 opposed mucous surfaces of the segments look- 

 ing toward the ileum are covered by villi and 

 present the structure of the small intestine. In 

 foetal life the other two surfaces possessed yilli 

 too, but by birth the latter have disappeared. 

 The surfaces turned toward the large intestine 

 present the follicles and glands of Lieberkuhn 

 peculiar to the large intestine. 



The function of the valve is to prevent re- 

 gurgitation of intestinal contents back into the 

 small intestine. When the caecum is distended, 

 the segments are approximated. They act even in the cadaver, proving that 

 muscular action is not essential. When in an experiment water was injected 

 into the colon, not a drop passed through the valve ; when the pressure was 

 increased to a height of two or three metres the valves did not yield, but the 

 walls ruptured. In intestinal obstruction there is evidence of a return of con- 

 tents from the large intestine. This is probably due to a slow, gradual disten- 

 tion of the walls of the large intestine, and hence a relative insufficiency of the 

 valve. High enemata may pass this valve in two out of three cases, but such a 

 valve is regarded as imperfectly developed and incompetent from the first. 



FIG. 655. Vertical section through the 

 caecum and ileo-caecal valve. (Gegen- 

 baur.) Col. Colon. C. Caecum, pv. Pro- 

 cessus vermiformis. 



