THE EYE. 749 



ment, would be intelligible, and the almost inexplicable correspondence 

 in the size of the images of the smallest distinguishable interspaces be- 

 tween two objects, with the diameter of the "rods" and "cones," be 

 placed in its true light. I consider it impossible to say anything with 

 respect to the import of the other elements of the retina, for although 

 the "granules" may be compared to minute bipolar ganglion-corpuscles, 

 and their continuity with the radiating fibres is known, this affords as 

 little ground for discussion as to their function, as is given by the know- 

 ledge of the fact that the large nerve-cells of the inner layers have nu- 

 merous processes and probably free terminations. 



The vessels of the retina are derived from the art. centralis retince, 

 which enters the eye enclosed in the optic nerve, and begins to ramify 

 from the centre of the colliculus ncrvi optici in 4 or 5 main branches. 

 Lodged at first only beneath the membrana limitans, these vessels pene- 

 trate through the layer of nerve-fibres into that of gray nerve-substance, 

 ramify in an elegant arborescent manner as far as the ora serrata, and 

 pass by their terminal prolongations on all sides into a rather wide- 

 meshed network of very fine capillaries (0-002-O003 of a line), which is 

 lodged chiefly in the gray layer, but partly also in the expansion of the 

 optic nerve. In animals, the veins commence with a complete circle, 

 circulus venosus retince, at the ora serrata, accompany the arteries in 

 single trunks, and converge to the vena centralis, which quits the eye 

 together with the artery. No large vessels exist in the "yellow spot," 

 where there are only numerous capillaries. I have never yet met with 

 nerves on the retinal vessels, whilst on the outside of the larger vessels 

 I have occasionally noticed traces of an accompanying fibrous tissue, ap- 

 proaching nearest to the embryonic, reticular connective tissue. 



The radiating fibre-system of the retina, though known in its separate 

 parts to older and more recent observers, had not been comprehended 

 in its connection, and we are very greatly indebted to H. Mu'ller for his 

 accurate investigations into this important structure in animals of every 

 class. I have repeated Mailer's observations in the human eye, which 

 was not investigated by him, and have been enabled to confirm in it all 

 that he has stated, and in some respects to carry the observations fur- 

 ther. The reason why the radiating fibre-system and the relation of 

 the " rods" to it has hitherto remained unknown, is because no one ex- 

 cept Bowman, so far as I am aware, has engaged in the indispensable 

 study of vertical sections of the retina, and moreover, because no one 

 had thought of applying chromic acid to that tunic, which has elsewhere 

 in the nervous tissues been of such important service, and although I 

 had particularly shown that the multipolar retinal cells were well pre- 

 served in it. If parts still fresh be taken for examination, in transverse 

 sections and chromic acid preparations, very satisfactory views of the 



