138 Peculiar Structure in the Eyes of Fishes. 



If the cornea of a cod-fish, pike, whiting, mackerel, &c. be 

 removed, the eye remaining in situ, and the iris carefully 

 stripped off, a small roundish body, slightly stained with the 

 usual pigment, will be seen attached to one point of the cir- 

 cumference of the crystalline capsule, where it is surrounded 

 by that portion of hyaloid membrane, analogous to the ante- 

 rior layer of the canal of Petit, in Mammalia. The opposite 

 extremity of this body, or its apex, for it is somewhat pear- 

 shaped, is attached to the posterior and external margin of 

 the iris, or at the junction of that membrane with the choroid. 

 A delicate fibril of nerve, stained with pigment, proceeds 

 downwards and backwards from this body, between the fis- 

 sure in the retina of these animals, which extends from the 

 optic nerve, to its anterior termination. 



The connection of the pyriform body with the lens is not 

 immediate, but by the interposition of a fine, transparent, and 

 highly elastic ligament, possibly a portion of the hyaloid mem- 

 brane, to which it closely adheres. 



At a point immediately opposite to the implantation of 

 this body, the circumference of the lens is firmly bound to 

 the vitreous body, and intermediately to the junction of the 

 circumference of the iris with the choroid membrane, by a 

 highly elastic, tough, very strong and transparent membrane, 

 capable of supporting the whole weight of the eye : it seems 

 to be gradually shaded off on each side, into the hyaloid mem- 

 brane investing the circumference of the crystalline capsule. 



Owing to the slight convexity of the vitreous body anteri- 

 riorly, the fixed circumferential points, both of the pear-shap- 

 ed body, and of the elastic membrane, or ligament, opposite, 

 are posterior to their insertions into the crystalline capsule ; 

 hence, if any action like that of contraction were to take place 

 in this body, the lens would be drawn slightly backwards, 

 and its focal relation altered. Upon a cessation of the con- 

 traction, the lens would be restored to its place, by the re- ac- 

 tion of the elastic ligament. 



The relative situation of this body may be determined in 

 the following manner. If the gill-covers of the fish, (cod or 

 pike), be removed, and an imaginary line, (D E, Jig. 16), be 

 drawn from the nostril to the superior articulation of the 

 hranchicB, and another line, (F G), cutting it at right angles, 

 drawn through the centre of the eye, this body will be found 

 placed in the under and anterior quarter into which the eye 

 will be thus artificially divided. In this diagram, A indicates 

 the position of the pear-shaped body; B, the elastic ligament 

 opposite ; C, the iris, partially removed. 



