14 CLASSIFICATION OP FISHES. 



structure of the mouth may be thus described : — The 

 inter- maxillary bone, in most fishes, forms the edge of 

 the upper jaw, behind which is the os labiate, or max- 

 illary ; a palatine arch, composed of the palatine, the 

 two pterygonian processes, a jugal bone, a tympanic and 

 squamose bone, constitutes, as in birds and reptiles, a 

 sort of interior jaw, and supplies, behind, an articula- 

 tion to the lower jaw, which has, in general, two bones 

 on each side. In such fish as have teeth, these pro- 

 cesses are varied in innumerable ways : they are found, 

 for instance, on the inter-maxillaries, the maxillaries, 

 the lower jaw, the vomer, the palatines, the tongue, the 

 arches of the gills, and even on certain bones, behind 

 the latter, called by Cuvier ossa pharyngis. 



(17-) A ^ ew ofner anatomical characters may be 

 briefly noticed. The nostrils are situated between the 

 eye and the end of the muzzle or upper jaw, and are 

 usually double, that is, opening by two perforations on 

 each side. The eyes are usually rather large for the 

 size of the body ; but in some types they become very 

 small, in which case they are always situated on the top 

 of the head, and are then termed vertical ; the cornea 

 is very flat, the aqueous humour small in quantity, 

 while the crystalline is nearly globular, and very hard. 

 The tongue is small, hard, and bony; so that the taste 

 enjoyed by fishes, must be very trifling.* The stomach 

 and intestines present nothing essentially peculiar : in 

 the generality of fishes, the pancreas is represented 

 either by cceca of a peculiar tissue, situate round the 

 pyloris, or by this tissue itself, at the commencement of 

 the intestines : the kidneys are placed on the sides of 

 the spine ; but the bladder, contrary to what is seen in 

 quadrupeds, opens behind the anal and the generative 

 organs. The majority of fishes are oviparous ; but the 

 cartilaginous order, and a few others representing them, 



* This sense, indeed, is rendered almost unnecessary, for the great ma. 

 jority of fishes swallow their food whole. This is one of the great charac- 

 teristics of the fissirostral type of birds; and as the fishes represent the 

 same type in the circle of the Vertebrata, we are accordingly prepared to 

 expect such coincidence. 



