1179 



the mesentery. This fold, in the majority of cases, is more or less triangular in 

 shape, and as a rule extends along the entire length of the tube. Between its two 

 layers and close to its free margin lies the appendicular artery (Fig. 1073). The canal 

 of the vermiform process is small, extends throughout the whole length of the tube, 

 and communicates with the cecum by an orifice which is placed below and behind 

 the ileocecal opening. It is sometimes guarded by a semilunar valve formed by a 

 fold of mucous membrane, but this is by no means constant. 



Structure. The coats of the vermiform process are the same as those of the intestine : serous, 

 muscular, submucous, and mucous. The serous coat forms a complete investment for the tube, 

 except along the narrow line of attachment of its mesenteriole in its proximal two-thirds. The 

 longitudinal muscular fibers do not form three bands as in the greater part of the large intestine, 

 but invest the whole organ, except at one or two points where both the longitudinal and circular 

 fibers are deficient so that the peritoneal and submucous coats are contiguous over small areas. 



The circular muscle fibers form a much thicker layer than the longitudinal fibers, and are 

 separated from them by a small amount of connective tissue. The submucous coat is well 

 marked, and contains a large number of masses of lymphoid tissue which cause the mucous 

 membrane to bulge into the lumen and so render the latter of small size and irregular shape. 

 The mucous membrane is lined by columnar epithelium and resembles that of the rest of the 

 large intestine, but the intestinal glands are fewer in number (Fig. 1074). 



\ 



* Muscular coat 



Columnar 

 ' epithelium 



_ Glands 



FIG. 1074. Transverse section of human vermiform process. X 20. 



The Colic Valve (valvulacoli; ileocecal valve) (Fig. 1075). The lower end of the ileum 

 ends by opening into the medial and back part of the large intestine, at the point 

 of junction of the cecum with the colon. The opening is guarded by a valve, 

 consisting of two segments or lips, which project into the lumen of the large intes- 

 tine. If the intestine has been inflated and dried, the lips are of a semilunar shape. 

 The upper one, nearly horizontal in direction, is attached by its convex border 

 to the line of junction of the ileum with the colon; the lower lip, which is longer 

 and more concave, is attached to the line of junction of the ileum with the cecum. 

 At the ends of the aperture the two segments of the valve coalesce, and are continued 

 as narrow membranous ridges around the canal for a short distance, forming the 

 frenula of the valve. The left or anterior end of the aperture is rounded; the right 

 or posterior is narrow and pointed. In the fresh condition, or in specimens which 

 have been hardened in situ, the lips project as thick cushion-like folds into the lumen 

 of the large gut, while the opening between them may present the appearance of a 

 slit or may be somewhat oval in shape. 



slit or mj 



