420 



DIGESTIVE SYSTEM OF THE HORSE 



the first part of the duodenum closely to the liver and the right dorsal part of the 

 colon; the remainder is somewhat less closely attached by it to the base of the 

 csecum and right kidney, the sublumbar muscles, and (more closely) to the terminal 

 part of the great colon and the first part of the small colon. ^ 



The mesenteric part, or jejuno-ileum, has been conventionally subdivided into 

 the jejunum and ileum, but no distinct point exists at which to make the demarca- 

 tion. With the exception of the origin and the last two or three feet, the mesen- 

 teric part of the intestine varies so much in position that only a general statement 

 can be made. It lies in numerous coils, mingled with those of the small colon, 

 chiefly in the dorsal part of the left half of the abdomen, from the visceral surface 

 of the stomach to the pelvis. It may insinuate itself between the left parts of the 

 colon and the abdominal wall; also between the ventral parts of the colon, reaching 



Fig. 359. — Topography of Viscera of Mare; Left View. 

 I.R., First thoracic vertebra; I.L., first lumbar vertebra; 2.K., second sacral spine; 5., scapula; A., humerus; 

 5/., sternum; B., ilium; 0., femur; L., lung in complete expiration; I., dotted Une indicating contour of lung in in- 

 spiration; /f., pericardium; Z., costal part of diaphragm; Z'., tendinous center of diaphragm; LiV., left kidney; l.v.C, 

 left ventral colon; v.Q., sternal flexure of colon; d.Q., diaphragmatic flexure of colon; Z>., small intestine; Af., small 

 colon; xV., rectum; a, coccygeus muscle; b, retractor ani; c, c, sphincter ani externus; ti, constrictor vulvse; e, sacro- 

 coccygeus ventralis; /, anterior gluteal artery; g, internal pudic artery; h, abdominal wall in section. (After Ellen- 

 berger, in Leisering's Atlas, reduced.) 



the floor of the abdomen. In some cases coils of it lie against the right flank when 

 the caecum contains little material. The terminal part of the intestine (ileum) 

 passes to the medial (left) surface of the csecum and joins the lesser curvature of 

 its base. The average diameter of the jejuno-ileum is about two and a half to three 

 inches (ca. 6 to 7 cm.). In the cadaver one often finds much of the tube presenting 

 irregular constricted and dilated parts which are not to be regarded as permanent 

 conditions. The last three or four feet (ca. 1 m.) are usually tightly contracted, 

 resembling somewhat the terminal part of the CBSophagus. This part may be termed 

 the ileum. 



The mesenteric part is connected with the dorsal abdominal wall by the great 

 mesentery. This is a wide, fan-shaped fold, consisting of two layers of peritoneum, 



1 It will be noticed that the mesoduodenum is not continuous with the great mesentery, but 

 ends by a free edge. The mesentery begins on the opposite surface of the end of the duodenum, 

 so that the bowel is attached by two peritoneal folds at this point. 



