■f 



THE DUODENUM 



1161 



anterior glandular proventriculus, and a posterior muscular gizzard with a horny lining 

 serving to grind the fodd. The mammalian stomach is the most variable in form and 

 structure which are correlated with the method and character of aUmentation. The cardiac 

 end of the stomach is often lined to a variable extent with a prolongation of the oesophageal 

 stratified squamous epithelium. The three kinds of glands, cardiac, fundic and pyloric, are 

 typically present. In general, the stomach is larger and more complicated in herbivora than 

 in carnivora. Instead of being a single sac, the stomach may be more or less divided into 

 chambers. An incomplete division into cardiac and pj-loric portions is so common that it may 

 be considered typical. The most extreme specialization is found in the ruminants. In 

 these the stomach has four chambers, the first two of which, however, are expansions of the 

 oesophagus. 



THE SMALL INTESTINE 



The small intestine [intestinum tenue] extends from the pylorus to the ileo- 

 caecal orifice, and occupies most of the abdominal cavity below the liver and 

 stomach. It is a cjdindrical tube whose diameter decreases from about 4 cm. 

 above to about 2.5 cm. at the lower end. Its length, when removed from the 

 body and measured fresh, averages about 7 metres (23 ft.) ; but when formalin- 

 hardened in situ, the length (which is probably nearer that during life) is onl}' 

 about 4 metres. The length does not seem to vary according to sex, height or 

 weight in the adult, but it is said to be relatively longer in the child. 



The small intestine includes two main divisions, the duodenum and the 

 mesenteric small intestine, the latter being further subdivided into jejunum and 

 ileum. 



THE DUODENUM 



The duodenum is the first part of the small intestine, and is verj- definite in 

 position and extent. It is firmly attached to the posterior abdominal wall, being 

 almost entirely retroperitoneal. It is the widest part of the small intestine, the 



Fig. 920. — The Duodenum and Pancreas, Anterior View. 

 Superior layer of transverse meso-colon 





i 



Duodeno-jejunal fiexure 



Inferior layer of transverse meso-colon 



Inferior part of duodenum 



Superior mesenteric vessels 



average width being 4 cm. or more, and is also the shortest segment, being only 

 about 25 cm. in length. In general, it is somewhat C-shaped, the concavity 

 enclosing the head of the pancreas (figs. 920, 921, 922). 



Parts. — For convenience of description, the duodenum is divided into the 

 following parts: (1) the first or superior portion [pars superior] which is short 

 (5 cm. or less), leading from the pylorus and forming the superior flexure [flexura 

 duodenalis superior]; (2) the descending portion [pars descendens], about 7 or 8 

 cm. in lengthy which receives the bile and pancreatic ducts and joins the inferior 

 portion at the inferior flexure [flexura duodenalis inferior]; and (3) the inferior 

 portion [pars inferior], which is again subdivided into (a) transverse portion [pars 

 horizontalis], about 10 cm. long, which usually ascends slightly and passes 

 gradually into (b) the ascending portion [pars ascendens], 2 or 3 cm. long, ter- 

 minating in the duodeno-jejunal flexure [flexura duodenojejunalis]. 



