PISCES. 93 



The frontal bone is composed of six pieces ; the parietal of 

 three ; the occipital of five ; five pieces of the sphenoides and 

 two of each temporal bone, remain, in the composition of the 

 cranium. 



Besides the usual parts of the brain which are arranged as 

 in Reptiles one after the other, Fishes have knots or ganglions 

 at the base of their olfactory nerves. 



Their nostrils are simple cavities at the end of the muzzle 

 almost always perforated by two holes, and regularly lined by 

 a plaited pituitary membrane. 



The cornea of their eye is very flat, and there is but little 

 aqueous humour, but the crystalline is very hard and almost 

 globular. 



Their ear consists of a sac representing the vestibule, in 

 which are suspended small bodies most commonly of a stony 

 hardness, and of three membranous semi-circular canals, situ- 

 ated in the cavity of the cranium rather than in the substance 

 of its parietes, the Chondropterigii excepted, in which they 

 are entirely contained in them. The eustachian tube and 

 tympanal bones are always deficient, and the Selachians alone 

 have a fenestra ovalis which is level with the head. 



The sense of taste in Fishes can have but little energy, as a 

 great portion of the tongue is osseous, and frequently furnished 

 with teeth and other hard parts. 



The body in most of them is covered with scales, and none 

 possess organs of prehension ; the fleshy cirri of some may 

 supply the imperfection of the other organs of touch. 



In the greater number, the intermaxillary bone forms the 

 edge of the upper jaw, having behind it the maxillary, termed 

 the labial bone. A palatine arch, composed of the palatine 

 bones, of the two pterygoid processes, the zygomatic process, 

 the tympanum and squamous portion, forms, as in Birds and 

 Serpents, a sort of anterior jaw, and furnishes, behind, an ar- 

 ticulation for the lower jaw, which generally has two bones on 

 each side ; the number of these pieces, however, is reduced 

 in the Chondropterygii. 



Teeth are found in their intermaxillary, maxillary, lower 

 jaw, vomer, bones of the palate, on the tongue, on the arches 



