338 FISHES. 



There is, moreover, in a great number of fishes a falciform liga- 

 ment (e, fig. VIII) which passes by a furrow of the retina and 

 penetrates into the vitreous, of which it is the only bond. This liga- 

 ment arises at the entrance of the optic nerve, and follows the interior 

 concavity, descending towards the base of the eye ; it contains the 

 vessels and ner/ves : its inferior point, nearest the uvea, is attached to 

 the capsule of the crystalline by its inferior surface, sometimes by 

 means of a simple prominence or a lamina a little more opaque ; some- 

 times, as is observed in the tunnies, by means of a species of gran- 

 ular body or transparent tubercle, and harder than thevitreous into 

 which it is inserted.* There are fishes, such as the salmon, and 

 herrings, in which this ligament is opaque and black,like the internal 

 surface of the ruyschian ligament. 



In the chondrupterygians this ligament does not exist, neither does 

 it exist in many of the malacopterygians, especially the carps. 



In the conger are perceived two very small ligaments, one placed 

 anteriorly and the other posteriorly, which support the crystalline as 

 by means of two poles. 



There are four and even five tunics in the eyes of fishes. The most 

 external ( f, f), or the sclerotic, is thick, fibrous, supported in part, 

 in most species, by two cartilaginous pieces, inserted into its tissue, 

 and which have a space between them posteriorly ; they are more or 

 less ossified in large fishes, and even in certain species, for example in 

 the sword-fishes, they form for themselves a spherical envellope com- 

 pletely ossified, Avith the exception of the orifices for the entry of the 

 nerve and the encasement of the cornea. 



In the chondropterygians the sclerotic is destitute of these pieces ; 

 it is uniformly cartilaginous ; in the rays and squalus, its cartilage 

 has posteriorly a prominence for articulation with the pedicle which 

 supports the globe. In common fishes its fibrous part frequently 

 assumes a thickness posteriorly, and forms a tuberosity. 



The anterior opening of the sclerotic' forms a frame for the cornea, 

 which is there inserted into a circle frequently a little thicker. The 

 cornea is lamellated as in the other classes, and its internal lamina is 

 sometimes coloured with yellow or green, as is seen in the perch. 



Under the sclerotic is first, in many fishes, a cellular tissue of a 

 greasy nature (g g, fig. iv.), of a greater or less extent, and which 

 sometimes forms a thick layer. It is wanted in the cod and in other 

 species, but it is very thick in the scioenas : in the perch it forms 

 different lobes in the circumference of the globe. 



be removed the surfaces appear fibrous or grooved. The fibres are arranged in five 

 different modes, the same mode being found invariably in the same animal. In the 

 greater proportion of lenses of all animals the structure is symmetrical, in relation 

 to the anterior or posterior surfaces, or to the poles of the axis of vision. How- 

 ever there are some fishes which present a remarkable deviation from this law, by 

 having the anterior surfaces having their fibres arranged according to one mode, 

 whilst those of the posterior assume some other plan. The Doctor supposes that 

 this is intended as a means of correcting the aberration. — Eng. Ed. 



* This is what Mr. Jurine names the cristalline ganglion. Only having seen it 

 in two eyes changed by the spirit of wine, he supposed it to be opaque. 



