102 



made up of the Distal Cell layer (fig. 29, D. c. I.) and 

 Outer Interstitial Cells (fig. 30, In. c. o.). Tkis is Patten's 

 outer ganglionic layer and tke Ganglienzellenscliiclit of 

 Kawitz (36). 



[h] The layer of Eod Cells (Retinophorae — Stabchen- 

 zellen(fig. 29, i?. 6'.). 



(c) The layer of Rods (Stabchen) (fig. 29, R.). 



The cells of the inner ganglionic layer of Patten, 

 corresponding to the Zwischenzellen of Hesse, and ^hat I 

 shall call the inner interstitial cells, are to be found 

 between the rod cells (fig. 30, /. c. i.). 



Rod Cells. — With regard to the minute histology of 

 these structures much confusion exists. They form the 

 most conspicuous portion of the retina in transverse 

 sections, and are prominent as a layer of columnar cells, 

 the basal proximal ends of which are continued as the 

 rods forming another well-defined layer of the retina. 



The rod cell layer is thus the middle layer of the 

 retina, lying between the layer of rods and the distal layer 

 of cells, to be considered below. The rod cells are of 

 considerable length, and decrease gradually in thickness 

 towards the periphery of the retina until, indistinguishable 

 from nerves, they become connected with the fibres of the 

 inner branch of the optic nerve (fig. 29, Op. n. i.) which 

 pass down outside the optic vesicle on all sides and unite 

 to form the nerve branch under the eye. In order to 

 study the details of a rod cell, seciions must be cut in the 

 plane of the retina and at right angles to the long axis of 

 the eye-stalk. An examination of teased preparations is 

 also necessary in addition to the sections. 



The rod cell increases gradually in diameter from a 

 mere thread at the back of the retina to the typical 

 columnar region. At about a fourth of its length is a 

 slight varicosity, and a short distance further and nearer 



