Dissection of the Eye of the Streaked Bass. 217 



The retina consists of two layers, a fibrous* and a pulpy. A 

 vascular or a serous cannot be demonstrated. There is a division at 

 its lower part from the entrance of the optic nerve to its termination 

 at the iris. The optic nerve is folded up like the ruffle of a shirt, 

 and if it be pulled after the sheath is divided, the retina may be drawn 

 through the foramina in the coats. 



There appears no aqueous humor. What is contained in the an- 

 terior chamber, communicates with and has the same cel'ular struc- 

 ture as the vitreous humor. The membranes of the vitreous humor 

 pass off in rays from the edge of the choroid and from the capsule of 

 the crystalline. There is no appearance of Petit's canal. 



The crystalline lens is spherical, completely surrounded by the 

 vitreous humor ; as usual it increases in density towards the centre. 

 When immersed in a solution of corrosive sublimate, it gradually be- 

 comes white but it is not acted upon like albumen. When the lens of 

 a sheep is allowed to remain in a solution of corrosive sublimate, scarce- 

 ly any change is perceptible and consequently it is not albuminous. 

 According to Berzelius the composition of the crystalline lens resem- 

 bles that of the red globules of the blood. In fishes, the blood pass- 

 es through the ramifications of the posterior portion of the choroid 

 gland ; the red globules appear to be taken up by the other portion, 

 to pass in a tortuous direction over the choroid and to be deprived 

 of their coloring matter before passing to the lens. In animals that 

 live in air, the choroid alone seems capable of preparing what the 

 lens requires. 



At the inferior axis of the crystalline lens and attached to its cap- 

 sule, is a small triangular body having its inner surface covered with 

 pigmentum nigrum. It adheres to a cord placed at the divided por- 

 tion of the retina. It passes through the loop in the iris and is in- 

 serted into the vitreous humor behind the crystalline. Its mechan- 

 ism may be seen by inspecting the plate, fig. 3. When the portion 

 a part of which passes through the loop, is brought into action, the 

 vitreous humor is drawn forwards and the lens is pushed before it. 

 When the other portion acts, the lens is drawn backwards. 



* A fibrous coat may be exhibited in the retina of a bullock by immersing an 

 eye for a few days in alcohol, pouring a solution of corrosive sublimate on the 

 retina and separating the fibres by a camels hair pencil. Four coats may thus be 

 demonstrated, a vascular, a fibrous, a pulpy and a serous. 



Vol. XXVII.— No. 2. 28 



