PHYSIOLOGICAL ANATOMY OF THE LARGE INTESTINE. 259 



brane is provided with tubules and closed follicles, the latter frequently 

 being very abundant. This little tube generally contains a quantity of clear, 

 viscid mucus. The uses of the vermiform appendix are unknown. 



Ileo-ccecal Valve. The opening by which the small intestine commu- 

 nicates with the caecum is provided with a valve, known as the ileo-caecal 

 valve, situated at the inner and posterior portion of the caecum. The small 

 intestine, at its termination, presents a shallow concavity, which is provided 

 with a horizontal, button-hole slit opening into the caecum. The surface of the 

 valve which looks toward the small intestine is covered with a mucous mem- 

 brane provided with villi and in all respects resembling the general mucous 

 lining of the small intestine. Viewed from the caecum, a convexity is 

 observed corresponding to the concavity upon the other side. The caecal 

 surface of the valve is covered with a mucous membrane identical with the 

 general mucous lining of the large intestine. It is evident, from an exami- 

 nation of these parts, that pressure from the ileum would open the slit and 

 allow the easy passage of the semi-fluid contents of the intestine ; but press- 

 ure from the caecal side approximates the lips of the valve, and the greater 

 the pressure the more firmly is the opening closed. The valve itself is com- 

 posed of folds formed of the fibrous tissue of 

 the intestine, and circular muscular fibres from 

 both the small and the large intestine, the whole 

 being covered with mucous membrane. The lips 

 of the valve unite at either extremity of the slit 

 and are prolonged on the inner surface of the 

 caecum, forming two raised bands, or bridles ; 

 and these become gradually effaced and are thus 

 continuous with the general lining of the canal. 

 The posterior bridle is a little longer and more 

 prominent than the anterior. These assist some- 

 what in enabling the valve to resist pressure from 

 the caecal side. The longitudinal layer of mus- 

 cular fibres and the peritoneum pass directly 

 over the attached edge of the valve and are not 

 involved in its folds. These give strength to 

 the part, and if they be divided over the valve, 



,. - n ja -, IT i 



gentle traction Will SUmCe to draw OUt and Obllt- 



, , , i , , , , , 



erate the folds, leaving a simple and unprotected 



,. i , JIT -i,i -n 



communication between the large and the small 

 intestine. 



Peritoneal Coat Like most of the other abdominal viscera, the large 

 intestine is covered by peritoneum. The caecum is covered by this mem- 

 brane only anteriorly and laterally. It usually is bound down closely to the 

 subjacent parts, and its posterior surface is without a serous investment; 

 although sometimes it is completely covered, and there may be even a short 

 mesocaecum. The ascending colon is likewise covered with peritoneum only 

 in front, and is closely attached to the subjacent parts. The same arrange- 



.^.-opening of the ^aiiint 

 tine into the C(Kcum &* Eon ^ 



small intestine; 2, ileo - csecal 

 valve ; 3, caecum ; 4, opening of 

 the appendix vermiformis ; 5, 



mucous fold at the opening o^ 



the appendix ; 6, large intestine ; 



7, 7, folds of the mucous mem- 



