SECT. 226.] 



GREY LAYERS OF RETINA. 



557 



Fig. 228. 



in a variable amount between the elements of the granular layer, 

 from which it is rather sharply marked off, and the fibres of the 

 optic nerve, from which it is less abruptly defined. It everywhere 

 consists of two portions : 1, an outer layer finely granular and 

 finely fibrillated (the layer of the grey nerve-fibres of Pacini) ; 

 and, 2, of an inner lamina of multipolar nerve-cells. These 

 have exactly the same characters as those of the brain, varying 

 between o'oo^" to o , oi6'" in size; they are mostly pyriform or 

 roundish, or are drawn out into three to five angles ; and they all 

 possess one to six and even more long pale branched processes, first 

 observed by Bowman 

 (see Lectures on the Eye, 

 p. 125), similar to those 

 of the central nerve-cells. 

 In all cases where these 

 nerve-cells are seen upon 

 perpendicular sections, 

 one to two of these pro- 

 cesses proceed outwards, 

 and are lost in the inner 

 granular layer (see be- 

 low) ; while the others 

 run horizontally, and are 

 in part continued into 

 genuine varicose optic 

 fibres (Corti, Remak, H. 

 Midler, and myself), in 

 part connect together the more remote nerve-cells (Corti, confirmed 

 in one instance by my own observation). The nuclei of these 

 nerve- cells, which behave towards re-agents like those of the cells 

 of the brain, measure , 003'" to o"005'", and generally possess a 

 very distinct nucleolus. The outer finely granular layer of grey 

 substance consists of a finely granular matrix, containing nothing 

 else than the outer processes of the nerve-cells, together with the 

 continuations of the fibres of Midler from the rods and cones into 

 the innermost parts of the retina. This stratum measures o"Oi5'" 

 to o"026"' in thickness, while the nerve-cells form a layer 0*045" 

 to 0^05 2'" thick at the yellow spot, where they are densest, and 

 hence the layer of the cells decreases in thickness as it is traced 

 forwards, until, at last, the cells occur qiiite isolated. 



4. Internal to the above layer follows the expansion of the optic 

 nerve (fig. 225, 7). In its course from the optic commissure (see 



Two nerve-cells from the human retina, magnified 300 

 times. The smaller with two processes outwards, and only 

 one varicose nerve- fibre arising from it; the other with a 

 dividing process which passes into three nerve fibres, and 

 two similar processes torn off. 



