ABDOMINAL CAVITY 339 



point where the vermiform process joins the caecum, and 

 they terminate in the complete stratum of longitudinal muscle 

 of the rectum. The longitudinal muscle of the rectum forms 

 a complete covering, but is not of uniform thickness ; on the 

 contrary it is much thicker on the anterior and posterior 

 aspects of the rectum than it is on the sides. In the anal 

 canal the longitudinal muscular stratum passes between the 

 external and the internal sphincters, and terminates in the 

 skin at the margin of the anal orifice. The circular stratum 

 of muscle, as in the case of the small intestine, forms a com- 

 plete and continuous covering throughout the whole length 

 of the large intestine, but it is most distinct in the constric- 

 tions between the sacculi. At the lower end of the anal 

 canal it is greatly increased in thickness to form the internal 

 sphincter ani. 



The Mucous Membrane of the large intestine, as already 

 pointed out, is entirely devoid of the plicae circulares and 

 villi, which are such prominent features of the mucous mem- 

 brane of the small intestine. Its internal surface, however, is 

 not perfectly smooth, but is raised into numerous transverse 

 and oblique ridges which can be obliterated by extension of 

 the gut. 



As in the case of the small intestine, the mucous mem- 

 brane of the large intestine contains enormous numbers of 

 tubular intestinal glands, whose orifices can be seen with the 

 aid of a low-power lens. It contains no aggregated lymph 

 nodules, but embedded in it are numerous solitary lymph 

 nodules which project into the submucous layer. 



Structure of the Vermiform Process. The vermiform pro- 

 cess differs in structure from the main part of the large 

 intestine in some important respects. Its serous layer is 

 practically complete and is not provided with appendices 

 epiploica. Its longitudinal stratum of muscle forms a complete 

 covering. Its mucous membrane is relatively thin and the 

 intestinal glands are poorly developed, but the most striking 

 differential feature is the enormous amount of lymphoid tissue 

 in the submucous layer. The lymphoid tissue is deposited 

 in the form of nodules, of relatively large but varying size, 

 which are so closely packed together that they form a 

 practically continuous layer between the circular muscle 

 and the mucous membrane. 



The remaining portions of the large intestine will be 



