236 PISCES. 



Salmon, Perch, and Flounder. Still, however, papillae similar to 

 those of the human subject have been found upon the smooth mucous 

 membrane, e. g. in Mugil cephalus. The mucous membrance lining 

 the stomach is usually soft as velvet, forms delicate reticulations, but 

 is rarely provided with papillae and projecting folds. Occasionally, 

 as in Uranoscopus scaber, we meet with clusters of secerning follicles 

 within the intestinal caeca. 



The structure of the intestinal canal in the Plagiostomi, or Rays 

 and Sharks, merits a separate consideration, though an extremely 

 near approach to it is made by the Sturgeon. They have a short 

 but wide oesophagus, continued into a large oval stomach that is 

 furnished with muscular layers ; to this wide gastric cavity succeeds 

 a narrow intestiniform canal, which may be viewed either as the 

 cardiac portion of the stomach or the duodenum ; in its place we 

 find, in the Sturgeon, a larger loop of intestine. In some instances, 

 and perhaps these are very rare, there would appear to occur, e. g. 

 Squalus maximus, a more compound kind of stomach than is usually 

 observed in the class of Fishes. In this Shark the stomach is par- 

 celled out by constrictions and inversions into several divisions, the 

 first of which is separated from the oesophagus by two large trian- 

 gular valves, and the fourth division by a strong internal pyloric 

 projection from the remainder of the intestine. This latter, in the 

 Sturgeon and Plagiostomi, is very wide, and (with some modifica- 

 tions peculiar to the different species that can not. be considered in 

 this work) distinguished by a singular structure that is developed in 

 its interior. The mucous membrane here projects in the form of a 

 plate that winds spirally like a staircase as far as the very anus, 

 and in this way the extent of the absorbent surface of the intestine, 

 which throughout its course is very short, becomes much increased. 

 Posteriorly where it is continued into the cloaca the intestine narrows, 

 and presents to our notice, as in Squalus canicula, a small coecal ap- 

 pendage. 



We have yet to consider, as occurring in many Osseous Fishes, a 

 peculiar set of caecal canals developed from the pylorus, and that 

 are known under the name of Pyloric appendages. These caeca were 

 formerly viewed as the analogues of the pancreatic gland, which is 

 actually absent as a true parenchymatous viscus in many Fishes. 

 The propriety, however, of thus interpreting the pyloric appendages 

 is rendered doubtful by the fact, that these organs have been found 

 in Fishes, e. g. the Trout, in which there exists also a compact 

 pancreatic gland. The pyloric appendages are invariably absent in 



