FISHES. 25 



of tlie mouth, is usually very short, and furnished internally with 

 longitudinal folds. It is often difficult to distinguish the stomach 

 from the oesophagus, which directly passes into it, and to assign 

 precisely the limit of the two. In some, as in the genus Cyprinus 

 and in Cobitis fossilis, there is no distinction. 



The gullet (pharynx) is constantly surrounded by a layer of 

 circular fibres, a true sphincter muscle, behind the ossa pharyngealia. 



In some fishes, as the pike, the stomach has an elongated form, 

 wider in the middle, and the pylorus is situated at the posterior 

 extremity, opposite to the superior orifice. In others the stomach 

 is reflected at an angle or arch, the cardiac portion (pars cardiaca) 

 being divided from the pyloric by a constriction, and the latter 

 towards its extremity where it passes into the intestine is sensibly 

 narrower, whilst the former preserves nearly the same width 

 throughout. Such, for example, is the form of the stomach in 

 Cyclopterus lumpus. The most usual form however of the fish's 

 stomach is that where the cardiac portion is prolonged into a blind 

 sac below, whilst the pyloric portion lies transversely above this 

 last on the right side of the stomach, like a narrower portion of 

 intestine ; such a stomach is found for instance in Lophius piscato- 

 rius, Scicena aquila, &c., and, amongst our fresh-water fishes, in 

 the perch. The muscular membrane of the stomach is always 

 thinner than that at the commencement of the oesophagus, and con- 

 sists of longitudinal and circular fibres. 



With very few exceptions there exists at the pylorus an annu- 

 lar fold or membranous valve, which indicates the commencement 

 of the small intestine. The distinction between the small and the 

 large intestine is not always very obvious ; the circumference of the 

 posterior part of the intestine is not always larger, sometimes even 

 smaller than that of the so-called small intestine. Almost never is 

 there to be found a trace of a coecum at the commencement of the 

 large intestine, but often (at least in the osseous fishes) an annular 

 membranous valve, like that of the pylorus, is met with at the termi- 

 nation of the small intestine. The intestinal canal is of very various 

 length, more or less convoluted ; on the whole, however, it is short. 

 In Petromyzon, Syngnathus, Belone, and some others, it holds an 

 entirely straight course, without any flexure from the mouth to the 

 vent. In the sharks and rays also the canal is short, but here a 

 membranous valve of a spiral form, present also in the sturgeons 



