288 THE RETINA, BY MAX SCHULTZE. 



also by indirect vision. I therefore retract my earlier view, which I 

 consider to be no longer tenable. We, however, habitually see 

 through another yellow screen present throughout the whole extent of the 

 retina, namely, the narrow -meshed plexus of its capillary vessels, which 

 lie in front of all the percipient elements, that is to say, between the 

 limitans interna and the external granulated layer. The quantity of 

 the rays of the spectrum which a single layer of corpuscles sometimes 

 standing on their edges, and disposed like rouleaux of coin, absorbs is 

 very considerable, as an examination with Browning's spectroscope 

 shows. The hoernoglobin lines are visible, and a considerable portion 

 of the rays at the violet end of the spectrum are lost. With thicker 

 layers of blood corpuscles, like those circulating in the larger retinal 

 vessels, the absorption effects would clearly be much more considerable. 

 And, although there are many holes in this screen of bloodvessels 

 through which we may see, and of which, on account of the constant 

 movements of the eye, we are unconscious ; yet the plexus of blood- 

 vessels, especially if it be projected from the various layers of the 

 retina into one plane, is too thick for its influence to be entirely dis- 

 regarded. Alterations in the blood affecting this absorption power 

 for certain luminous rays must necessarily lead to unusual perceptions 

 of colour.* 



5. ORA SERRATA AND PARS CILIARIS. 



The neighbourhood of the ora serrata of the human retina, 

 in opposition to the area surrounding the macula lutea, is 

 characterized by the gradual disappearance of the nervous 

 elements, whilst the connective tissue, on the contrary, is pro- 

 gressively more and more developed. The radial supporting 

 fibres, with the spongy network connecting them, form the 

 principal portion of the tissue at the ora serrata ; and ulti- 

 mately, though in a somewhat modified condition, appear to 

 constitute that continuation of the retina over the ciliary pro- 

 cesses which no longer participates in the perception of visual 

 images. 



H. Muller has made such extensive researches upon this sub- 

 ject, that little remains for subsequent inquirers to add. His 

 results show essentially that the " several layers of the retina 



* Zeitsclirift fur wissenscliaft. Zooloyie, Band viii., p. 91. 



