THE SMALL INTESTINE 



421 



Hepatic'^ 

 duct 



Pancreo/ic 

 duct 



between which the vessels and nerves reach the bowel; it also contains the mesen- 

 teric lymph glands and some fat. The visceral border of the mesentery contains 

 the intestine, while the parietal border or root of the mesentery (Radix mesenterii) 

 is attached to a small area around the great mesenteric trunk under the first and 

 second lumbar vertebrae. The root is thick, as it contains a large nmnljer of vessels 

 and nerves placed close together. The mesentery is short at first, but soon reaches 

 a length of one and a half to two feet (ca. 50 cm.)— sufficient to allow coils of the 

 intestine to reach the abdominal floor, the pelvic cavity, or even to descend into 

 the scrotum through the inguinal canal. Near its termination the intestine leaves 

 the border of the mesentery, so that the latter has a free edge which passes to the 

 csecum. Thus there is formed the ileo-csecal fold (Plica ileocajcalis), which at- 

 taches the ileum to the lesser curvature of the caecum. 



Structure. — The wall consists of four coats — serous, muscular, submucous, and 

 mucous. The serous coat is complete except at the mesenteric edge, where the 

 vessels and nerves reach the bowel. The muscular coat consists of an external 

 longitudinal and an internal circular layer, the latter being the thicker. In the 

 last few feet of the intestine the muscular coat is very thick, and being usually 

 firmly contracted in the dead subject, gives the impression that this part of the bowel 

 is of smaller caliber; such, however, is 

 not the case during life. The sub- 

 mucous coat is a layer of areolar tissue 

 in which the vessels and nerves ram- 

 ify. It contains also the duodenal 

 glands and the bases of the solitary 

 and aggregated IjTnph nodules. The 

 mucous membrane is soft and vel- 

 vety. It has a grayish or yellowish- 

 red color and is very vascular. About 

 five or six inches from the pylorus it 

 forms a pouch, the diverticulum duo- 

 deni, in which the pancreatic and he- 

 patic ducts open. On a small papilla 

 nearly opposite this is the termina- 

 tion of the accessory pancreatic duct. 

 At the ileo-ceecal opening the mucous 

 membrane projects slightly into the 



cavity of the csecum, forming the ileo-csecal valve. The free surface is thickly 

 beset with villi, small projections of the mucous membrane which can be seen well 

 by placing a piece of the membrane in water. They are relatively short and thick 

 in the horse. Each contains a central lymph-vessel (lacteal), and around this a 

 plexus of capillaries, lymphoid tissue, and unstriped muscle-fibers. They are im- 

 portant agents in absorption from the contents of the intestine. The epithelium 

 is columnar, with many goblet cells. Underneath the basement membrane is a 

 layer of unstriped muscle-fibers, the muscularis mucosae. The glands of the small 

 intestine are of two kinds; their secretion is termed the succus entericus. 



1. The intestinal glands (Glandulse intestinales) are present throughout. They 

 are simple tubular glands which open between the villi. 



2. The duodenal glands (Glandulae duodenales)^ are present in the first 

 twenty feet or more (ca. 6 to 7 m.) of the bowel. They are branched tul}ulo- 

 alveolar glands, and are situated in the submucosa, so that their ducts perforate 

 the muscularis mucosae and the mucous membrane. 



1 These were formerly known as Brunner's glands, but in the B. N. A. are termed glandulae 

 duodenales. On account of their extension beyond the duodenum and their submucous position, 

 EUenberger has suggested the name glandute submucosae. 



Diverticulum 

 duodeni 



360. — Diagram of Section of DivERTicuLrM duo- 

 deni OF Horse. 

 Solid line indicates mucous membrane; muscular and serous 

 layers are not shown. 



Fig. 



