728 THE EYE. 



as are also some, at least, of those of the outer layer, namely, the pyriform 

 bodies supporting the cones. But, according to recent investigations of 

 Henle, whose statements have been corroborated by Ritter as holding good 

 in the mammals generally, the bodies which constitute the bulk of the outer 

 nuclear layer, are elliptical corpuscles, which, when perfectly fresh, exhibit 

 transverse striation similar to muscular fibre, to the extent of three dark 

 lines alternating with clear substance in each, but which soon break up into 

 globules. 



Fig. 478. Fig. 478. STRIPED ELLIPTICAL CORPUSCLES OP THE EXTERNAL NUCLEAR 

 LAYER OF THE RETINA (from Henle). ^-p 



The internuclear layer, which lies between the layers now 

 referred to, is a clear space of unequal depth, vertically striated, 

 and having likewise a molecular appearance. The molecular 

 basis is more marked in a thin stratum which intervenes be- 

 tween the internal nuclear layer and the nerve-cells, and which, 

 therefore, has been distinguished as the molecular layer. 



3. Nervous layer. a. The cellular layer consists of nerve-cells with a 

 fine molecular material interspersed among them. At the bottom of the 

 eye over the yellow spot they are thickest (from 8 to 10 cells deep), and 

 decrease in quantity in front ; so that at a fifth of an inch from the ora 

 serrata they are only scattered in clusters. Around the entrance of the 

 optic nerve there is only a single stratum of these elements. The cells whon 

 fresh are transparent and nucleated, being roundish or pear-shaped in out- 

 line, and are furnished with from two to six ramified offsets. By their 

 internal offsets the cells are continuous with the nerve-fibres beneath ; by 

 horizontal offsets they are united one with another ; and by those which 

 pass outwards they are connected with the corpuscles of the internal nuclear 

 layer. 



6. The nerve-fibre layer consists of nerve-fibres directed forwards from the 

 optic nerve, and collected into small bundles, which, compressed laterally, 

 intercommunicate and form a delicate web with narrow elongated meshes. 

 This stratum diminishes in thickness forwards, and ends at the ora serrata : 

 it forms a continuous membrane, except at the yellow spot, where the nerve 

 fibres are wanting. According to Bowman, the fibres, which lose their dark 

 outline on reaching the retina, consist there of an axis-cylinder only. It is 

 now well established that they terminate in the nerve-cells on which they 

 lie, and this is the only mode of their termination which has been fully 

 ascertained. 



c. Membrana limitans and connective tissue. The limiting membrane lines 

 the inner surface of the retina, separating it from the vitreous body. It is 

 an extremely thin and delicate membrane, which can be detached in shreds; 

 and it agrees with the other glassy membranes of the eye-ball in not being 

 affected by alkalies, maceration, or boiling. On its retinal surface it is 

 studded with the broadened insertions of vertical threads of connective tissue, 

 which separate the nerve-fibres into bundles, ar,d form the inner parts of the 

 Miillerian fibres. Nuclei apparently exist both in these and in the mem- 

 brana limitaus itself. Delicate homogeneous connective tissue, likewise, 

 enters into the composition of the layers of the retina as far outwards as the 

 bases of the rods and cones, and gives there the appearance of a horizontal 

 line, the external limitary membrane of Schultze. 



4. Radiating fibre s of Multer, and connections of the different elements of the 

 retina. From the foregoing description it will be gathered that the history of 



