FISHES. 47 



formed of flat cells (pavement-epithelium). The scales contain a 

 considerable quantity of phosphate of lime (in well-dried scales 

 it often forms forty per cent, of their weight), and a much smaller 

 quantity of carbonate of lime ^ 



Taste in fishes appears to be very small. The part named 

 tong-ue in fishes consists merely of the anterior extremity of the 

 tongue-bone covered by mucous membrane. Besides, this part is 

 often armed with teeth, and possesses no proper muscles, so that it 

 is moved in conjunction with the branchial arches alone. The 

 glosso-pharyngeal nerve supplies it with no branches, but is distri- 

 buted chiefly to the first branchial arch, although another branch, 

 usually smaller, is spread upon the palate. If fishes possess the sense 

 of taste, the palate, rather than the tongue, would appear to be its 

 seat. 



The organ of smell is commonly placed in front of the eyes on 

 each side, on the upper surface of the head ; in the Cyclostomes and 

 AonpMoxus alone it is single or unpaired. In LopMus piscatorius 

 the organs of smell appear as two small cups attached by a pedicle 

 to the upper lip. The interior of their cavity is covered by mucous 

 membrane, with folds at the bottom which radiate from a centre, or 

 which form transverse strise proceeding on each side from a middle 

 axis. In the osseous fishes each nasal cavity has usually two aper- 

 tures, one in front and one behind. Except in the Myxino'ids the 

 cavity of the nose has no communication with that of the mouth, as 

 is the case in vertebrates that breathe by lungs. 



Tlie eyes of fishes, the soles (the genus Pleuronectes) excepted, 

 are situated on each side of the head, often more above, sometimes 

 quite at the side, as in the hammer-fishes [Zygcenoi). The bony orbit 

 is not perfectly closed, but open forwards and backwards. The 

 eye-ball is commonly flatter in front and irregularly convex behind. 

 Although capable of little motion, it has still six muscles in most 

 fishes, four straight and two oblique, as in man. In some fishes the 



^ Compare on the structure of fishes' scales Agassiz (Poiss. foss.), Mandl {Ann. 

 des Sc. nat. ie S4ne, Tom. xi. 1839, p. 347, and the objections of Agassiz ibid. Tom. 

 XIV. 1840, pp. 98 and foil.), and Peters in Mueller's Archiv, 1841, Jahreshcrlcht, 

 s. 209 — 216. In the Ganoids, where the scales are covered by an enamel, microscopic 

 investigation indicates bone-corpuscles {lacuna), like those which occur in bone. See 

 Williamson On the microscop. struct, of the scales and dermal teeth of some r/ano'id and 

 pi aco'kl fishes, Phil. Tr. 1849, pp. 435—475, with plates. 



