PISCES. 719 
hne from the head to the tail. Sensation appears to be weak in almost all 
the class, although some, as the eel, possess irritability after being cut into 
small portions. 
The nostrils in fishes are simple cavities or hollows at the point of the 
suout, in the interior of which are disposed lamine in a radiated form. 
These cavities are often divided into two compartments, and sometimes, as 
in the lamprey, the two nostrils are united into one. The eye is possessed ofa 
very flat cornea, with but little aqueous humor ; but the crystalline lens is 
almost globular, and very hard. In general, the eyes of fishes are large .n 
proportion to their size, and they are destitute of eyelids. The pupil, or the 
opening by which light penetrates into the eye, varies much in form. In 
the greater part of the species of which the eyes are vertical, anatomuists 
remark a singular disposition of the pupillary orifice, which presents the 
fringes of the iris arranged in such a manner, as to dilate or contract, in order 
to weaken or augment the quantity of light which enters the eye. In the 
Pleuronectes, both eyes are on the same side of the dorsal line. The ear 
consists of a sac which represents the vestibule, in which are suspended 
bones of a stony hardness, and of three semicircular, membranous canals, 
situate rather in the cavity of the cranium, than in the substance of its 
walls, except among the Chondropterygu. There is neither eustachian 
tube, nor tympanum, and bones ; and the order Selachz have only an oval plate, 
on a level with their head. It is probable that the vibrations of the water 
may communicate a sensation analogous to that of sound. The sense of 
taste in fishes cannot be delicate, as their tongue is often osseous, and 
furnished with teeth or other hard covering; they are destitute of salivary 
glands, and the greater part swallow their food without maceration, 
Neither is the sense of touch very acute, as in most, the body is covered 
with scales, and in all, the organs of prehension are wanting. ‘The cirri, or 
filamentous, fleshy processes of some families, may, perhaps, supply the im- 
perfections of their organs of touch. In the greater number of fishes, the 
intermaxillary bone forms the margin of the upper jaw, having behind it 
the maxillary or labial bone. The palatine arch, composed of the palate 
bones, the two pterygoid processes, the zygomatic process, the tympanum, 
and the squamous portion, forms, as in birds and serpents, a kind of interior 
jaw, and furnishes behind, an articulation for the lower jaw, which has two 
bones on each side ; but these pieces are reduced to the smallest number in 
the Chondropterygii. The teeth of fishes present many varieties. Some 
have none at all, and in others the jaws are so hard that they form a kind 
of solid beak ; in some, these teeth are pointed, edged, crenated, flat; and 
in others, they are placed on the lips, the jaws, the palate, the tongue, the 
gullet, or in all these parts at the same time. The stomach is almost 
always simple, and the intestinal canal short, as in carnivorous animals; 
the liver is very large; and there is but one opening for rejected matters, 
the milt of the male, and the ova of the female. 
