820 PRELIMINARY ANATOMICAL AND HISTOLOGICAL OBSERVATIONS. 



discussed on p. 679. Between the two homogeneous limiting membranes (Ri and 

 Le) lies the supporting tissue of the retina (not true connective-tissue). It in- 

 cludes the supporting fibers of Miiller (Fig. 268, Rf), which contain nuclei (k) 

 and pass through all the cerebral layers, and end in expanded terminations at the 

 internal limiting membrane (Rk). In addition, the supporting tissue forms a 

 network throughout all the retinal layers, with openings for the penetrating ner- 

 vous elements (Sg) . In the outer reticular layer, there are also flattened , partly 

 nucleated supporting cells, with long processes, and, at the optic-nerve entrance, 

 glia-cells. The inner segments of the rods and cones are also surrounded by a 

 basket-like supporting tissue. In the nerve-fiber layer there are flat, stellate cells. 

 From the ora serrata forward, the retina becomes suddenly thin, and, as the 

 ciliary portion of the retina, consists only of a layer of cylindrical cells, which 

 seems to have arisen from the coalescence of the -two nuclear layers, and is 



Pi. 



FIG. 269. Transverse Section of a Mammalian Retina 

 (after Ramon y Cajal): A, layer of rods and cones; 

 B, visual cells (outer nuclear layer); C, outer 

 reticular layer; E, bipolars (inner nuclear layer); 

 F, inner reticular layer; G, ganglion-cells; H, 

 nerve-fiber layer; a, rods; b, cones; e, a rod- 

 bipolar; f, a cone-bipolar; r, lower ramification 

 of the rod-bipolar; f, lower ramification of a cone- 

 bipolar; g, h, i, j, k, ganglion-cells branching at 

 various levels in F; x, z, contact of rods and cones 

 with the bipolars; t, Miiller's supporting fibers; s, 

 centrifugal nerve-fiber. 



covered on the inner side by the limiting membrane 

 of the iris, a continuation of the internal limiting 

 membrane of the retina. This layer extends to the 

 posterior surface of the iris, as the iridic portion of 

 the retina. 



The blood-vessels of the retina lie in the inner 

 layers, as far outward as the inner nuclei. They 



communicate with the choroidal vessels only by fine branches at the optic- 

 ance; they are surrounded by perivascular lymph-channels. The 



TfcT* er ol the capillaries run internally to the inner nuclear layer. 



ine lovea centralis has no vessels. Except in the mammalia, the eel, and several 



ret^aca^StlStoi. retina C ntainS n Vessds at alL Dest ction of th e 



FIG. 268. Layers of the Retina. 



J 6tina 4 has an acid reacti n, but becomes alkaline if kept in the 

 -BlotalM ds and cones contain albumin, neurokeratin , nuclein, and colored 



m the cones): so-called chromophanes. 

 same constituents as the gray matter of the brain. 



than 



The other layers have the 



* t 5 ans P arent - elastic capsule, which is thicker anteriorly 

 and is lined on the inner surface of its anterior portion by a 



