PHYSIOLOGICAL ANATOMY OF THE LARGE INTESTINE 22/ 



inch (2.54 centimeters) in length, turns backward to terminate in the 

 anus. 



The caecum, or caput coli, presents a rounded dilated cavity continu- 

 ous with the colon above and communicating by a transverse slit with 

 the ileum. At its lower portion is a small cylindrical tube, opening 

 below and a little posterior to the opening of the ileum, called the 

 vermiform appendix. This is covered with peritoneum and has a mus- 

 cular and a mucous coat. It is sometimes free and sometimes provided 

 with a short fold of mesentery for a part of its length. The coats of the 

 appendix are very thick. The muscular coat consists of longitudinal 

 fibres only. The mucous membrane is provided with tubules and closed 

 follicles, the latter frequently being very abundant. This little tube 

 usually 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 buttonhole slit, opening into the caecum. 

 The surface of the valve which looks toward the small intestine is 

 covered with a mucous membrane 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 examination of these parts, that press- 

 ure from the ileum opens the slit and allows the easy passage of the 

 semifluid contents of the intestine ; but pressure 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 composed 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, form- 

 ing two raised bands, or bridles ; and these become gradually effaced 

 and are thus continuous with the general lining of the canal. The pos- 

 terior bridle is a little longer and more prominent than the anterior. 

 These assist somewhat in enabling the valve to resist pressure from the 

 caecal side. The longitudinal layer of muscular 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 are divided 

 over the valve, gentle traction suffices to draw out and obliterate the 



