86 SUPPLEMENT ON 



urinary bladder are likewise contained in a fold of the peri- 

 toneum- 

 There are two remarkable openings on each side of the 

 anus in many fishes, such as rays, squali, sturgeons, lam- 

 preys, salmon, &c. ; through which the interior membrane of 

 the peritoneum becomes continuous with the epidermis, and 

 assumes a mucous character : two other openings, at least in 

 rays and squali, extend this continuity to the pericardium 

 and entire lining membrane. The intestinal canal is com- 

 posed of the same tunics, and the variations they suffer, 

 and folds they form, are analogous to those of other ver- 

 tebrated animals. The internal folds of the oesophagus 

 are in general longitudinal ; its cavity is prolonged to the 

 bottom of the cul-de-sac of the stomach. Sometimes, as in 

 labri, this cul-de-sac is wanting ; and instead, there is only a 

 slight dilatation of the canal ; but more commonly the stomach 

 forms a bend, or gives off from a part somewhere near the en- 

 trance on the right side the branch which terminates at the 

 pylorus. This branch running transversely, or even upwards, 

 sometimes, as in salmon, thymallus, and mugil, becomes in the 

 tunic of such muscular density, as to assume the character of 

 a true gizzard. 



The conditions of the ventricular sack are infinitely varied; 

 the thickness of the membranes, and folds, &c. would de- 

 mand separate articles to be fully discussed. The intestinal 

 canal varies in like manner in breadth, length, and folds ; is 

 more or less dense, villous, &c. ; but there is never a ccecum, 

 as in quadrupeds. One of the most remarkable folds in the 

 intestines of fishes is the spiral valve of rays, squali, and stur- 

 geons. Near the pylorus, many species have ccecal appendices, 

 sometimes in considerable number, within the doublings of 

 which a viscous liquor appears to be generated, supplying, it 

 is supposed, the office of the pancreas; and as fishes are in 



