128 Comparative Anatomy of the 'ElcBric Organs of the 



Rays, as is well known, are flat fifh, the peroral fin of 

 which is prolon";ecl anteriorly on the fules of the head by 

 means of a cartilage that borders its circumference. The 

 torpedo differs from other fiflies of the fame genus by a very 

 confiderable interval between this cartilage and the head. 

 All this large vacuity is tilled up by prifnis of fix, five, and 

 fometinies four planes. Thefe prifms adhere by their bafes 

 to the (kin above and to that below. They are arranged 

 parallel to each other, follow the projeiSting and irregular 

 contours of the head and branchiae, and externally form a 

 femi-clliplic (Iratum. When the. Ikin is removed, all thefe 

 prifms, the bafes of which are then obferved, exhibit the ap- 

 pearance of a honey-comb. They are fo many fmall tubes 

 filled with a fubrtance which by chemical analyfis I found to 

 be a compound of gelatin and albumen. The texture of 

 thefe tubes is aponeurotic, and they are united to each other 

 by a kind of lax reticulation formed of tendinous fibres which 

 envelop them in every direftion : in the lafl; place, they are 

 covered and fliut by an aponeurotic membrane, and above 

 thefe coverings the Ikin is applied. This apparatus is fur- 

 niflied with nerves remarkable for their large fize. There 

 arc diftinguiflied four principal trunks, which are diftributed 

 to all the tubes, and which at length penetrate into their 

 fubftance and expand in it. 



Though ravs, in which the cartilage of the pectoral fin im- 

 mcdialcly borders the contours of the head, were not, like the 

 torpedo, in a condition to exhibit prifms or vertical tubes, 

 they did not differ from them fo much as might be expeded. 

 In the rays, r,s well as in the torpedoes, there iffues from the 

 cranium, a little before the ear, a nerve fo large that it fur- 

 pafl'es the volume of that which proceeds to the eye. This 

 nerve proceeds laterally, creeps over the fuperior face of the 

 inaffeter, and expands below, between that mufcle and the 

 firfl branchia, in a mafs which on the firfi: view might be taken 

 for a gland, but which is really the focus from which pro- 

 ceed, in feveral bundles, a great number of tubes analogous 

 to thofe of the torpedo. A bundle proceeds towards the 

 nofe, another fpreads over the belly, a third afcends on the 

 malfeter and terminates behind the occiput, and a fourth ex- 

 tends over the nnifcles of the perioral fin. In this refpeft 

 there are feme differences according to the fpecies : but thefe 

 tubes, in the ray as well as in the torpedo, always adhere to 

 the ikin above and to that below ; only, inllead of being ver- 

 tical, which is impoffible, for want of room, they follow the 

 contour of the head, extend over the moll exterior nuifcles, 

 and are longer according as they have a larger circuit td 



make 



