298 THE ANATOMY OF THE HORSE. 



feet ill length. It derives its name from its approximately straight course 

 through the pelvic cavity, in connection with which it will be more fully 

 described. 



Directions. — The coils of the jejunum and ileum should be arranged 

 in the left flank after the manner of Plate 41. To get a view of the 

 duodenum, the ca3cum should be thrown across the abdomen, with its 

 point towards the left side. The duodenum will then be seen encircling 

 the crook of the caecum on its outer side. Should the large intestine 

 contain much ingesta, that should be evacuated through an incision across 

 the pelvic flexure of the double colon and another at the point of the 

 caecum. When the ingesta has been expelled, the bowels should be 

 moderately inflated, and the cut ends ligatured. 



The Duodenum (Plate 44) is the first segment of the small intestine. 

 Its length is about two feet, but it cannot be very well seen in its 

 entirety at this stage of the dissection. It begins at the pyloric aper- 

 ture of the stomach, Avhere it is related to the posterior surface of the 

 liver. It curves upwards and backwards across the lower face of the 

 right kidney, and then sweeping round the crook of the caecum to its 

 outer side, it crosses the spine behind the anterior mesenteric artery, and 

 is continued as the jejunum. It is maintained in position by a narrow 

 band of peritoneum, and in this fixity of position it is distinguished from 

 the rest of the small intestine. 



The Jejunum and Ileum. These comprise the remaining portion of 

 the small intestine, of which about thirty feet is arbitrarily appor- 

 tioned to the former, and the remainder (about forty feet) to the latter. 

 They are arranged in the form of numerous coils, which occupy the 

 iliac, umbilical, and hypogastric regions. The coils are attached to 

 the free edge of a fold of peritoneum called the f/reat mesentery ; and 

 inasmuch as this mesentei-y is of considerable breadth, they may move 

 from place to place within the above-mentioned areas. When distended, 

 they have not a puckered, but a smooth, surface. The terminal part of 

 the ileum joins the crook of the caecum, into which it projects for a little 

 distance, after the manner of a tap into a barrel; and at the point of 

 entrance there is a valvular arrangement — the ileo-cacal valve, to pre- 

 vent regurgitation from the caecum into the ileum. 



The Peritoneum is the lining membrane of the abdominal and pelvic 

 cavities. It belongs to the class of serous membranes, and, like all such 

 membranes, it consists of a parietal and a visceral division, these being 

 portions of one great sac. The pai-ietal part is that which lines the 

 abdominal walls, or parietes ; the visceral part invests the solid and 

 hollow organs, or viscera, of the abdominal cavity. In virtue of this 

 membrane, all the free surfaces that present themselves when the 

 abdominal wall is removed, have a smooth and shining appearance. 

 The surface of the membrane is covered by a layer of endothelial cells, 



