THE ELASMOBRANCH FISHES 



135 



Stomach 



Tlie stoinacli of Elasmobranchs when seen in ventral view is a U- or J-shaped 

 tube (for types see figs. 173 to 175, c.s. and p.s.). the left arm of which, as in 

 Heptanchus, is the cardiac and the right arm the pyloric division. The great 

 variety in shape of the stomach found among the Elasmobranchs is due largely 

 to variation in the relative length of the pyloric arm. In some, although the 

 pyloric division is small in diameter, in length it 

 is practically equal to the cardiac (leopard shark, 

 fig. 173a; Raja); in others this arm is less than 

 one-half the length of the cardiac, so that the 

 shape of the stomach in these is better described 

 as a J (Acanthias) . In still others the pyloric limb 

 is onl,y a small projection from the cardiac divi- 

 sion of the stomach (Scynmus licliia, fig. 135b ; 

 Laemargus rostratus, fig. 136b). In the latter 

 there is a so-called "blind sac" (sc.-) at the angle. 



The mucous lining of the adult stomach is 

 thrown into folds which, as we have said, may be 

 continuous with those of the oesophagus. The folds 

 on the walls of the cardiac division are high and 

 may extend in part as the finer folds into the py- 

 loric limb, but those of the two regions are usually 

 distinct. 



A section through the mucosa of the stomach of 

 Squalus acanthias according to Ringoen (1919; 

 fig. 134) shows a gland as long and flask-shaped. 

 The superficial epithelial cells (ejJ.) are somewhat 

 like those found in the oesophagus, that is, they 

 are columnar or pyramidal cells, the upper part 

 of which contains a plug of mucus (pi.). The cells 

 lining the median part of the crypt are large and 

 their nuclei are vertical in position. In the deeper 

 crypts are the gastric cells that are peculiar to the 

 cardiac stomach. They lie at the base of the crypts and are large and granular 

 and of a polygonal shape with their nuclei taking a more or less horizontal 

 position. These are the true peptic cells (pc), which secrete the digestive 

 substances. 



The function of gastric juice, which contains hydrochloric acid and a fer- 

 ment, pepsin, is the digestion of protein matter. Such digestion takes place at 

 a much lower temperature in the stomach of the shark than in the stomach of a 

 higher animal. While, in the latter, digestion is carried on at body temperature 

 (37° C), in the former it takes place at 10° to 15° C, although the pepsin may 

 also be active at as high as 40° C. 





Fig. 134. Section through lin- 

 ing of the stomach, Squalus 

 acanthias. (From Eingoen.) 



ep., epithelial cell ; pc, pep- 

 tic cells; ph, mucous plug. 



