STRUCTURE OF THE LARGE INTESTINE 431 
thick and consists of large bundles which are rather loosely united. A large band, 
the recto-coccygeus, is detached from it on either side, and passes upward and 
backward to be inserted into the fourth and fifth coccygeal vertebre. 
The submucous tissue is abundant in the wall of the rectum, so that the mucous 
membrane is loosely attached to the muscular coat, and forms numerous folds 
when the bowel is empty. 
The mucous membrane of the large intestine is thicker and darker in color 
than that of the small intestine. It forms large crescentic or semilunar folds 
Fig. 370.—Penvic Inter anp Posterior Part oF ABDOMINAL WALL OF Horse, VIEWED FROM THE FRONT. 
The left inguinal canal is partially opened. The peritoneum is retained except over a part of the left cremaster 
muscle. The sublumbar region is greatly foreshortened in this view. a, a’, Kidneys; a’’, adrenal; b., ureter; c, renal 
artery; d, aorta; e, stump of cceliac artery; f, stump of anterior mesenteric artery; 9, posterior mesenteric 
artery; h, circumflex iliac artery; i, external iliac artery; &, internal iliac artery; J, spermatic artery in peritoneal 
fold (plica vasculosa), m; n, ductus deferens, enclosed in genital fold, 0; p, urinary bladder; g, round ligament of blad- 
der; r, middle ligament of bladder; s, rectum; ¢, margin of vaginal ring; u, posterior abdominal artery; 1, external 
pudie artery; w, rectus abdominis muscle; z, transversus and obliquus internus abdominis; y, y’, cremaster externus; 
z, posterior vena cava (cut). (After Ellenberger-Baum, Top. Anat. d. Pferdes.) 
(Plice semilunares), corresponding to the external constrictions. It has no villi 
nor duodenal glands. The intestinal glands are large and numerous. Solitary 
nodules are numerous, and there are aggregated lymph nodules at the apex of the 
cxcum and in the pelvic flexure and the adjacent portion of the left dorsal part of 
the colon. 
Vessels and ‘Nerves.—The arteries come from the anterior and posterior 
mesenteric and internal pudic arteries. The veins go to the portal and internal 
