FISHES. 335 



The chondropterygians differ little from oilier fishes, with respect 

 to the distribution of the nerves of the cranium ; but their nerves of 

 the pectoral arise from a much greater number of origins. At all 

 events we shall treat of their neurology in a more special manner 

 when we come to their history. 



CHAPTER VI. 



Organs of the external Senses in Fishes.* 



The senses of smell, sight, and hearing are conferred on fishes by 

 organs, analogous to those of other classes, and arranged in the same 

 manner: if their taste be feeble, there is nevertheless reason to be- 

 lieve, that it also resides in the covering of the tongue, unless the 

 singular tissues which are found in the palate of some species, such 

 as the cyprins, should also be regarded as the seat of it. As to the 

 touch, besides their general integuments the sensibility of which varies 

 to infinity, particular dispositions of certain parts, which become 

 more or less prolonged, and more or less moveable according to the 

 the species, furnished them with organs, which are often as sin- 

 gular, as they are remarkable. 



The Ei/e.f 



The eye in fishes is suspended in an orbit, of which the composition 

 has been already described, in the chapter on osteology; vaulted 



* Tlie organs of sight, hearing, and smell taken from the perch, are represented 

 pi. vii. viz: the nostrils fig. 11-; the eye from fig. iii. to viii. ; the ear fig. 9 

 and 10. 



f The folded membrane -which forms the optic nerve has been described and drawn 

 by Malpighi in the xiphias. 



The memoirs of Petit the physician, inserted in those of the Academy ef Sciences 

 for the years 1726 and 1730, contain several good observations on the eye of fishes. 

 In the memoirs of the latter year, he enters into details, respecting the forms and 

 curvatures of its parts, and partiexdarly of the crystalline lens of several salt and fresh 

 water fishes. Haller studied and described all the parts with accuracy, but only in 

 fresh water fishes, in the memoirs of 1762. His work presented with additions to 

 the Society of Gottingen in 1766 was reprinted in latin in his opera minora, vol. iii. 

 In this work, he describes the falciform ligament of the crystalline lens, the two 

 lamina of the retina, &e. : he takes the red body which lies between the ruyschian 

 and the selerotic for a muscle. 



Vicq d'Azyr, in his memoirs on fishes, does not speak of the eye ; and Monro con- 

 fines himself to a few details on its humours, considered in a dioptrical point of 

 view. 



I have added some facts in my lectures on comparative anatomy, vol. iii. in which 

 I have shown particularly the differences in the eyes of the chondropterygians; other 

 facts will be found in a. memoir of M. Rosenthal, printed in 1811, in the tenth 

 volume of the Archives Physiologiques de lleil. 



M. de Soemmering' sj sou gives, in his dissertation on the transverse section of the 

 eye, (Gottingen 1818, in folio,) five drawings of sections of the eye of the sturgeon, 

 the aiguillat, the ray, the cod, and the pike. 



Some useful facts will ( *uso be found in M. Angely's thesis on the eye and 



