CHAP. XVII.] STRUCTURE OF THE RETINA. 29 



Fig. 117. 





Vertical section of the Human Retina and Hyaloid Membrane, h. Hyaloid membrane. 

 h'. Nuclei on its inner surface, c. Layer of transparent cells, connecting the hyaloid and retina. 

 c. Separate cell enlarged by imbibition of water, n. Gray nervous layer, with its capillaries. 

 1. Its fibrous lamina. 2. Its vesicular lamina. 1'. Shred of fibrous lamina detached. 2'. Vesi- 

 cle and nucleus detached, g. Granular layer. 3. Light lamina frequently seen. (/.Detached 

 nucleated particle of the granular layer, m. Jacob's membrane, mf. Appearances of its particles, 

 when detached, m". Its outer surface. Magnified 320 diameters. 



the only nervous element of the retina existing over the extremity 

 of the optic nerve where it enters the globe a spot incapable of 

 vision. Immediately around this spot, the other layers commence 

 which have now to be described, and the first of these is the vesicular 

 gray layer. This layer is on the outer surface of the fibrous layer, 

 and so intimately blended with it, that it might almost seem as if 

 the fibres successively terminated in it. The vesicular layer is 

 thicker behind, and gradually thinner forwards. It very accurately 

 corresponds with the vesicular matter of the convolutions of the 

 cerebrum, consisting of a finely granular matrix with interspersed 

 very delicate vesicles, furnished with pellucid globular nuclei of 

 characteristic appearance. 



The blood-vessels of the retina, which are thickly distributed, 

 belong solely to the fibrous and vesicular layers now mentioned. The 

 central artery of the retina, after entering the globe in the axis of 

 the optic nerve, sends four or five radiating branches, which almost 

 immediately perforate the fibrous layer and spread out in a 

 beautifully arborescent manner, as a capillary network in the sub- 

 stance of the vesicular stratum. After slight maceration, it is easy 

 to wash the nervous material out of the meshes of the vessels ; and 

 they then form a vascular layer, but which it is hardly correct to 

 describe as a distinct lamina of the retina. They are merely the 

 nutrient vessels of the part, and are the representative of the close 

 network of the gray substance of the cerebral convolutions. Their 



