26o 



TWENTY- FOURTH LECTURE. 



cone granule lies sometimes higher, sometimes deeper (a) ; 

 we might say from necessity. 



We meet with still another 

 condition. In the peripheral 

 layers of the retina the cone 

 fibre passes through our mem- 

 brane in an ascending perpen- 

 dicular direction. The latter 

 now leaves this direction more 

 and more, to pass obliquely out- 

 wards and downwards (a). This 

 induces beneath the outer gran- 

 ular layer (that is the cone gran- 

 ules), a quite peculiar appear- 

 ance. 



Forwards, towards the ora 

 serrata, the retina increases in 

 thinness, and the nervous ele- 

 ments diminish ; the connective 

 tissue frame-work acquires the 

 upper hand more and more ; 

 finally all the nervous elements 

 have disappeared. 



By the ciliary portion of the 

 retina is designated a system 

 of cylindrical cells which lie on 

 the zonula Zinnii beyond the 

 ora serrata, and run as far as 

 the iris, according to many even to the pupillary border of 

 the latter. 



The blood-vessels of the retina, springing from the arteria 

 centralis, form an elegant wide-meshed reticulum of very fine 

 tubes. They occupy the inner portion of the retina, but pass 

 outwards to the inner granular layer, and perhaps still fur- 

 ther. The adventitia of the same surrounds the inner layer 

 but loosely, leaving a lymphatic space. 



It is impossible for us to enter into the exceedingly com- 



Fig. 207. — Cones from the macula lutea and 

 fovea centralis of man ; a, with decomposed 

 outer membrane ; l>, with the lamellar decom- 

 position of the same. 



