LAYERS OF THE RETINA. 41 



The gang-lion-cells of the retina may be classed into those the protoplasmic or peripheral 

 processes of which ramify in a diffuse manner in the inner molecular layer, and those the 

 protoplasmic processes of which are ramified horizontally in one or more of the strata of that 

 layer, where they interlace with similar ramifications from the cells of the inner nuclear layer. 

 The diffusely ramifying- cells (fig-. 50, VII., /) are usually small and with slender processes, and 

 this is also the case with some of the cells with stratified processes (fig. 50. v.. <i ; vi., e], but 

 many of the latter are larger, sometimes very large (giant cells), and with comparatively 

 coarse processes. 



The cells with stratified processes are classified by R. y Cajal according to the stratum of 

 the inner molecular layer in which these processes ramify. Some ramify, however, in two. 

 and even in more layers (bi- and multi-stratified). Three types of the stratified cells can 

 usually be distinguished. They mav be termed ///v.7. xc<-o/i<L and third, or from their relative 

 size, hirt/c. //'rfiini/. and xm/I, and some of each type appear to belong, as regards the dis- 

 tribution of their arborescence, to each stratum of the inner molecular layer. 



I-'irxt t !/]'. Those of the large type have a thick axis-cylinder process and one, two, or 

 more coarse protoplasmic processes, varying in vertical extent in different cells according to 

 the stratum of the inner molecular layer for which they are destined. Their terminal 

 arborescences extend over a considerable area, and are open in nature. The largest cells of this 

 type (giant cells) send their processes to the outer strata of the molecular layer (fig. 53, vii., 

 ii. c. c*) ; processes to the inner strata come from cells of the same type but of smaller size. 



Second type. The ganglion-cells of this type (fig. 50, vi., vn., /, y, A) vary in size of 

 cell-body, but are usually smaller than those of the first type, and of pyriform shape, the stalk 

 of the pear being directed outwards for a variable distance in the molecular layer according 

 to the position within this of the terminal arborescence. The latter is composed of moderately 

 fine varicose filaments which form a compact, closely interwoven ramification, occupying some 

 thickness of the molecular layer, the arborescence being less flattened out than is the case 

 with those from many of the cells of the first and third types. 



Third t;/jn'. This is represented by cells usually pyriform with small cell-bodies and 

 correspondingly fine moderately arborescent processes which may radiate from the end of a 

 straight outwardly directed stalk, as in the case of those which ramify in the outer strata of 

 the molecular layer (fig. 50, vi., )> or ma J spring in a similar radiating manner from the body 

 of the cell itself, as with those ramifying in the inner strata (fig. 50, vn.. b~). 



3. Inner molecular or inner plexiform layer, neurospongium. Next in 

 order to the ganglionic layer comes a comparatively thick stratum of a granular- 

 looking 1 substance, which as preparations treated by the methods of Ehrlich or of 

 Golgi show, is mainly made up of the arborescent terminations of the processes of 

 the cells in the layers which bound it internally and externally. A few branched 

 cells, apparently of nervous nature, occur within the layer (fig. 50, in.) ; these are 

 probably allied to the amacrine cells of the layer next to be described. The inter- 

 laced arborisations of the ganglion-cells, amacrine cells, and bipolars form within it 

 definite strata which, according to R. y Cajal, are altogether five in number. There 

 are a few blood-vessels in this layer, and the fibres of Muller pass through it as fine 

 vertical filaments with delicate lateral offsets. 



4. Inner nuclear layer. This is composed of a number of closely-packed 

 cells, which are frequently known collectively as the " inner granules," but are of 

 several distinct kinds. Some are bipolar nerve-cells, and it is the presence of these 

 which has led to the name ganglion retina being applied to this layer. They occupy 

 the bulk of the stratum and send processes inwards and outwards into the respective 

 molecular layers. Others are multipolar nerve-cells, the processes of which ramify 

 in the molecular layers ; they form incomplete strata close to and partly imbedded 

 in the molecular layers. Others, again, are nucleated enlargements belonging to the 

 fibres of Muller. The structure and arrangements of each of these elements must 

 be separately considered. 



a. Bipolar -celh. These, by far the most numerous, are round or oval clear cells 

 (fig. 50, i., in. ; fig. 51, 4), prolonged at either end into a fibre. 



Of the processes or fibres which proceed from these cells, the inner one, or that 

 extending into the inner molecular layer, is finer than the other, is always unbranched 

 until reaching that layer, and often exhibits varicosities similar to those on nerve- 



