INNER NUCLEAR LAYER OF THE RETINA. 43 



fibrils. It is regarded as the axis-cylinder process of the cell, and extends usually 

 to the inner part of the internal molecular layer, within which it ends in a terminal 

 ramification of varicose fibrils which is frequently in close proximity to the outer 

 surface of one or more of the ganglion-cells of the layer. The outer prolongation 

 or process of the bipolar cell is not varicose, is usually thicker than the inner one, 

 and in some cases passes undivided into the next layer, in others divides before 

 reaching it. Having arrived at the outer molecular layer it breaks up into an 

 arborisation within this layer, which is interlaced with arborisations of fibres 

 belonging to the horizontal cells presently to be described, and with the termina- 

 tions of the rod- and cone-elements of the bacillary layer. It has been shown 

 by R. y Cajal that the bipolars are of at least two kinds, distinguishable by 

 the character of the terminal arborescence of the outwardly-directed protoplasmic 



Fig. 50. ELEMENTS OF THE RETINA OF MAMMALS DISPLAYED BY THE CHROMATE OF SILVER METHOD 



OF GOLGI. (Cajal.) 



I. Section of the dog's retina, a, cone-fibre ; 6, rod-fibre and nucleus ; c, d, bipolar cells (inner 

 granules) with vertical ramification of outer processes destined to receive the enlarged ends of rod-fibres ; 

 e, bipolars with flattened ramification for ends of cone-fibres ; /, giant bipolar with flattened ramifi- 

 cation ; ff, cell sending a neuron or nerve-fibre process to the outer molecular layer; h, amacrine cell 

 with diffuse arborisation in inner molecular layer ; i, nerve fibrils passing to outer molecular layer ; 

 j, centrifugal fibres passing from nerve-fibre layer to inner molecular layer ; ra, nerve-fibril passing into 

 inner molecular layer ; n, ganglionic cells. 



II. Horizontal or basal cells of the outer molecular layer of the dog's retina. A, small cell with 

 dense arborisation ; B, large cell, lying in inner nuclear layer but with its processes branching in the 

 outer molecular ; a, its horizontal neuron ; C, medium sized cell of the same character. 



III. Cells from the retina of the ox. a, rod-bipolars with vertical arborization ; b, c, d, e, cone- 

 bipolars with horizontal ramification ; f, y, bipolars with very extensive horizontal ramification of 

 outer process ; h, cells lying on the outer surface of the outer molecular layer, and ramifying within it ; 

 i, j, m, amacrine cells within the substance of the inner molecular layer. 



IV. Neurons or axis-cylinder processes belonging to horizontal cells of the outer molecular layer, one 

 of them, b, ending in a close ramification at a. 



V. Nervous elements connected with the inner molecular layer of the ox's retina. A, amacrine cell, 

 with long processes ramifying in the outermost stratum ; B. large amacrine with thick processes 

 ramifying in second stratum ; C, flattened amacrine with long and fine processes ramifying mainly in 

 the first and fifth strata ; D, amacrine with radiating tuft of fibrils destined for third stratum ; E, 

 large amacrine, with processes ramifying in fifth stratum ; F. small amacrine, branching in second 

 stratum ; Gr, H, other amacrines destined for fourth stratum ; a, small ganglion-cell sending its 

 processes to fourth stratum ; 6, a small ganglion-cell with ramifications in three strata ; c, a small cell 

 ramifying ultimately in first stratum ; d, a medium sized ganglion-cell ramifying in fourth stratum ; 

 e, giant cell, branching in third stratum ; /, a bi-stratified cell ramifying in second and fourth strata. 



VI. Amacrines and ganglion-cells from the dog. A, amacrine with radiating tuft ; B, large amacrine 

 passing to third stratum ; C and Gr, small amacrines with radiations in second stratum ; F, small 

 amacrine passing to third stratum ; D, amacrine with diffuse arborisation ; E, amacrine belonging to 

 fourth stratum ; a, d, e, y, small ganglion-cells, ramifying in various strata ; i, f, large ganglion- cells, 

 showing two different characters of arborisation ; /, bi-stratified cell. 



VII. Amacrines and ganglion-cells from the dog. A, B, C, small amacrines ramifying in middle of 

 molecular layer ; b, d, y, h, i, small ganglion-cells showing various kinds of arborisation ; f t a larger 

 cell, similar in character to #, but with longer branch ; a, c, e, giant cells with thick branches ramifying 

 in the first, second, and third layers ; L, L, ends of bipolars branching over ganglion-cells. 



process, and by the position in the internal molecular layer in which the axis- 

 cylinder process terminates. In one kind this arborescence is composed of a 

 dendritic tuft of vertical fibrils, somewhat varicose and enclosing amongst them the 

 end-knobs of several (3 to 20) of the rod-fibres of the bacillary layer ; and the axis- 

 cylinder process ends in a varicose ramification over a body of a cell of the 

 ganglionic layer. These may be termed, therefore, the rod-bipolars, or bipolars with 

 vertical arborescence (fig. 50, i., c ; in., a). In the other kind (cone-bipolar s) this 

 terminal arborescence is horizontal (fig. 50, I., e ; in., b, c, d, e), and abuts against 

 or interlaces with the ramified foot of one or more cone-fibres, and the axis-cylinder 

 process usually extends to a less depth of the internal molecular layer, and is not 

 constant in position as is that of the rod-bipolar ; the axis-cylinder process of either 

 kind may give oif short collaterals in traversing the inner molecular layer. Some of 



