25 MIE VISULKA. 
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, /) 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 
