236 THE VISCERA. 



The inner surface of the stomach presents longitudinal folds 

 at its pyloric end and along the greater curvature as far as the 

 fundus. The prominence of these depends on the degree of 

 distension. Its walls are composed of an external peritoneal 

 layer, an internal mucous layer, and an intervening muscular 

 layer. This may be seen with the unaided eye in sections of 

 the wall. 



5. The Small Intestine. Intestinum tenue. The small 

 intestine lies in numerous coils which take up the greater part 

 of the space in the abdominal cavity. It has a length about 

 three times that of the body of the cat. It is usually considered 

 as. divided into three parts, duodenum, jejunum, and ileum ; 

 these divisions are, however, not clearly marked off. The 

 small intestine is suspended by the mesentery already 

 described. 



The duodenum is that part of the small intestine which fol- 

 lows the stomach. At the pylorus (Fig. 97, f) the alimentary 

 canal makes a rather sharp turn so that the first part of the 

 duodenum forms an angle with the pyloric portion of the 

 stomach, and extends caudad and slightly toward the right, 

 soon becoming directed almost entirely caudad and lying along 

 the right side. About eight or ten centimeters caudad of the 

 pylorus it makes a U-shaped bend, extending thus craniosinis- 

 trad for four or five centimeters. Here it passes without definite 

 limit into the jejunum, the duodenum being considered to end 

 at the next turn caudad. The entire duodenum is about four- 

 teen to sixteen centimeters in length. Between the two limbs 

 of the U-shaped bend formed by the duodenum, the duodenal 

 half of the pancreas is enclosed (Fig. 102, a). 



The walls of the duodenum are composed of the serous 

 (peritoneal) investment, a muscular coat which is made up of 

 an outer thin, longitudinal layer of fibres and an inner thick, 

 circular layer, a submucous coat, and inside this a mucous coat. 

 The mucosa is thrown up into numerous delicate finger-like 

 villi which give to it a velvety appearance. On the dorsal 

 wall of the duodenum, about three centimeters distad of the 

 pylorus, the mucosa presents a slight papilla, at the apex of 

 which is seen the oval opening of the ampulla of Vater. This 



