THE CECUM 



1301 



Structure of the Appendix (Fig. 1040). The coats of the appendix correspond to the coats 

 of the bowel serous, muscular (the outer layer of longitudinal, the inner of circular fibres), 

 submucous, and mucous. 



The outer or serous coat forms a complete investment for 

 the appendix except along the narrow line of attachment of its 

 mesentery in its proximal two-thirds or more. 



The longitudinal muscle layer is thin and irregularly distrib- 

 uted, and in certain regions may be exceedingly thin or actually 

 absent, so that the peritoneal and submucous coats are contiguous 

 over small areas. 



The circular muscle layer is a much thicker layer than the 

 preceding, and at the blind extremity forms a dome-like col- 

 lection of interlacing fibres. Both layers have openings at in- 

 tervals for the passage of bloodvessels. 



The submucous coat varies greatly in thickness. It contains 

 bloodvessels, nerves, and lymphatics, and a large number of 

 lymphoid follicles (300 to 400) and, at times, adipose tissue. 



The mucous membrane (Fig. 1038) is lined by columnar 

 epithelium and contains numerous solitary lymph follicles, glands 

 of Lieberkiihn (about 25,000), surrounded by diffuse lymphoid 

 tissue, bloodvessels, lymphatics, and nerves. 



The muscularis mucosae may be absent, may be scanty, or 

 may be distinct. The lymphoid follicles are visible to the naked 

 eye (Fig. 1038). Some of them are in the submucosa, some of 

 them chiefly in the mucosa, the bases of the latter, however, being 

 in the submucosa. 



The arteries of the cecum and appendix are derived from the 

 ileocolic branch of the superior mesenteric artery. Close to the 

 ileocecal junction the ileocolic artery gives off anterior and pos- 

 terior ileocecal branches to the terminal part of the ileum and 

 beginning of the large intestine. The terminal branches to the 



cecum are called anterior and posterior cecal arteries. The appendix is supplied by the 

 appendicular artery, a branch of the posterior ileocecal artery (see p. 665). 



The veins of the appendix are numerous, thin walled, and large. Veins from the submucous 

 plexus pass through the muscular gaps and enter the subperitoneal plexus. Veins from the sub- 

 peritoneal plexus pass into the veins in the mesoappendix which correspond to but do not really 



FIG. 1038. The internal sur- 

 face of the vermiform appendix. 

 (Bonaniy and Broca.) 



POSTERIOR 



iLEOCECAL 



ARTERY 



AND VEIN 



ILEAC BRANCH 



APPENDICULAR 



ARTERY AND 

 VEIN 



ASCENDING 

 COLON 



FIG. 1039. Arteries and veins of the cecum and vermiform appendix seen from behind. (Poirier and Charpy.) 



accompany the arteries (Lockwood). Most of the veins of the mesoappendix pass to the pos- 

 terior ileocecal vein, though some pass directly to the cecal vein. These veins are radicles of 

 the portal system. 



The lymphatics of the cecum and appendix are described on page 797. 



