364 PHYSIOLOGY 



CHAP. 



a firmer consistency, their colour, odour, and external characters 

 approximate to those of the faeces. 



On reaching the lower end of the ileum, the substances which 

 have accumulated and escaped absorption, are forced on by the 

 peristaltic movements through the cleft of the ileocaecal valve, 

 and pass into the large bowel. The lips of this cleft lie trans- 

 verse to the caecum, and are so arranged that the distension of 



- GO* 



CO 



FIG. 102. The caecum in connection with the ileum and colon. (Luciani.) The anterior external 

 wall of the caecum has been cut away to show the cleft and labra of the ileo-caecal valve, with 

 the orifice of the vermiform appendix, ci, fundtis of caecum ; av, vermiform appendix ; av', 

 its opening into the cavity of the caecum ; il, last tract of ileum ; v and v', lower and upper 

 labra, which circumscribe the cleft of the ileo-caecal valve ; co and co', first and second segment 

 of ascending colon. 



the caecum brings them together in the position of closure 

 (Fig. 102). The watertight closure of the ileocaecal valve be- 

 comes still more perfect when the peristaltic movements of the 

 large intestine begin in the fundus of the caecum. The content 

 of the caecum is then voided into the colon without any possibility 

 of reflux of faecal matter into the ileum, because the increase of 

 intracaecal pressure applies the lips of the valve still more firmly 

 together. This passage of the excreta from the small into the 

 large intestine has been regarded by some (Viault and Jolyet) as 

 a first, internal defaecation, in which the faeces, freed from all 

 useful constituents (like the exhausted residues on a filter) pass 



