THE EYE. 



743 



given off, which in many cases may be distinctly seen to proceed from 

 a pale border surrounding the granule, so that the whole is very like 

 a bipolar ganglion-cell in miniature. In Man, the granules, in the 

 greater part of the retina^ are disposed in two layers — an outer, thicker 

 of 0-013-0-OlG (A), and an inner, thinner (/), of 0-006-0-008 of a line 

 — which are parted from each other by a clear, fine-granular, and, to 

 some extent, vertically striated layer (r/), 0-006-0-008 of a line thick, 

 whilst, towards the ora serrata, the two constitute a single stratum 

 of not more than 0*015 of a line in thickness. The granules of the 

 inner layer are a trifle larger than those of the outer, and Avhen they 

 are oval, as is most usually the case, I find that they are placed with 

 the long axis in the direction of the thickness of the retina, so that their 

 processes, like those of the external layer, run directly outwards and 

 inwards. 



3. The layer of cineritious cerebral substance (Fig. 302 e) is pretty 

 sharply defined on the side of the granular layer, and less so towards 

 that of the fibres of the optic nerve, 

 between the elements of which it pene- 

 trates more or less. It is composed of 

 a finely granular matrix, corresponding 

 exactly with that of the gray substance 

 on the surface of the cerebrum and cere- 

 helium, and of numerous nerve-cells scat- 

 tered in it. Of the latter, some, parti- 

 cularly in the outer half of this layer, 

 which is 0-008-0-012-0-02 of a line 

 thick, are small (0-003-0.006 of a line), 

 inconspicuous, and in fresh preparations 

 recognizable only by their beautiful vesi- 

 cular nuclei; whilst another portion, 

 forming an almost continuous laver on 

 the inner side, are of a larger size 

 (0-006-0-016 of a line). These cells 



arc usually pyriform or rounded, or occasionally prolonged into 3-5 

 angles; and most of them, perhaps all, are furnished with pale pro- 

 cesses like those of the central nerve-cells — which were first noticed by 

 Bowman ("Lectures," &c., pp. 8-1 and 125), and afterwards also de- 

 scribed by Ilassall, Corti, and myself.* The processes occur either 

 single or in numbers varying from two to six and more ; are at first as 

 much as 0-002 of a line wide, but in their further course continually 



Fig. 305. — Nerve-cells wiili processes from the rc/ina of the Ox, magnified 350 diameters. 



* [Pacini appears to have been the fust to perceive the existence and true nature of 

 the caudate cells in this layer of tlic retina. ('■ Sulla tessitura int. dell. Retina,' 1844, p. 

 3-2.)— Trs.] 



