SECT. 227.] THE CRYSTALLINE LENS. 565 



their terminal twigs form a wide network of very fine (0*002'" to 

 to 0003 ") capillaries, which is chiefly seated in the layer of gray 

 nervous substance, and partly, also, in the expansion of the optic 

 nerve-fibres. The veins begin, in the lower animals, at the ora 

 serrata by an incomplete circle, circulus venosus retince, run with 

 their trunks parallel to the arteries, and collect in the t'gna centralis, 

 which leaves the eye by the side of the artery. At the yellow spot 

 there are 110 large vessels, but only numerous capillaries. I have 

 never seen nerves on the vessels of the retina; on the other hand, 

 I "find here and there traces of an accompanying fibrous tissue on 

 the outer side of the larger vessels, which is most closely allied to 

 embryonic reticulated connective tissue. 



With regard to the function of the retinal elements, I refer the reader to 

 my Mikr. Anat., ii. 2, § 281, and will here make only the following remarks: 

 I regard the rods and the cones as the only elements which can receive the 

 impression of light ; and I believe that they become endowed with this func- 

 tion through their connection with the nerve-cells, by means of the fibres of 

 Miiller acting as a conducting apparatus. The nerve-cells are to be looked 

 upon as a flat and expanded ganglion, and, in all probability, as constituting 

 the central organ of visual perception. This central apparatus and the brain 

 are then connected by a second conducting apparatus, the optic fibres, which 

 also have the function of placing the two retinae in connection with each 

 other. This view is based upon the demonstrated connection between the 

 elements of the bacillar layer and the nerve-cells, upon the want of a con- 

 nected layer of optic nerve -fibres at the yellow spot, and upon the absence of 

 any perception of light at the colliculus. My opinion is also supported by 

 the consideration, that we cannot possibly assign the faculty of perceiving 

 • light to the nerve-cells or to the granular layer, because the elements of these 

 are super-imposed in many layers, especially at the yellow spot ; and lastly, 

 the peculiar local arrangement of the rods and cones, their size corresponding 

 to the degree of the local sensibility of the retina, adds further confirmation 

 to my opinion. 



§ 22-7. The lens [lens crystalline?) is a perfectly transparent body, 

 connected at its posterior surface with the vitreous body, and 

 laterally with the zonula Zinnii, or the termination of the hyaloid 

 membrane. It is to be distinguished into the lens proper and its 

 capsule. 



The capsule of the lens {capsula leaf's) consists of two elements, 

 the proper capsule and the epithelium. The former is a perfectly 

 structureless, transparent, and very elastic membrane, which sur- 

 rounds the lens on all sides, like a mould, and separates it from 

 the neighbouring structures. If a lens with its capsule be laid in 

 water, a large quantity of the fluid is imbibed by the capsule. 



