66o 



SPECIAL SENSES 



The following description, with Fig. 169, was furnished by Loring : 

 " The arteries and veins of the retina are subdivisions of the arteria 

 and vena centralis. The larger branches run in the nerve-fibre layer 

 and are immediately beneath the inner limitary membrane. The vessels 

 lie so superficially that in a cross-section examined with the microscope, 

 they are seen to project above the general level of the retina, toward the 

 vitreous humor. While the large vessels are in the plane of the inner 

 surface of the retina, the smaller branches penetrate the substance of 

 the retina, to the inner nuclear layer. They do not extend, however, 

 as far as the outer nuclear and the layer of rods and cones. These 

 two layers, therefore, have no bloodvessels. 



" The ramifications of the 

 vessels present an arborescent 

 appearance when seen with the 

 ophthalmoscope. The manner 

 in which the vessels are distrib- 

 uted and the way in which the 

 circulation is carried on can be 

 better understood by a study of 

 Fig. 169 than by any detailed de- 

 scription. The figure represents 

 the ophthalmoscopic appearance 

 of a normal eye in young adult 

 life. The darker vessels are the 

 veins, and the lighter vessels, the 

 arteries. The dotted oval line is 

 diagrammatic and indicates the 

 position and extent of the macula lutea. It is seen that this oval space 

 contains a number of fine vascular twigs which, coming from above and 

 below, extend toward the spot in the centre of the oval, which marks 

 the position of the fovea centralis. In opposition, then, to the general 

 opinion, which is that the macula lutea has no bloodvessels, it is the 

 spot of all others in the retina which is most abundantly supplied with 

 minute vascular branches. These vessels can be distinctly seen even 

 with the ophthalmoscope ; and microscopical examination shows that 

 the capillary plexus in the macula lutea is closer and richer than in any 

 other part of the retina." (The figure shows an inverted image of the 

 right fundus.) 



The arteries of the retina send branches to the periphery, where 

 they supply a wide plexus of small capillaries in the ora serrata. These 

 capillaries empty into an incomplete venous circle, branches from which 

 pass back by the sides of the arteries, to the vena centralis. 



Fig. 169. Bloodvessels of the retina, x 75 (Loring). 



