450 



THE TISSUES, 



Fig. 294. 



These fibres radiate on all sides from the colliculus before men- 

 tioned, and constitute a continuous membraniform expansion ex- 

 tending as far as the or a serrata of the retina ; 

 presenting no considerable interruption, except 

 at the situation of the macula lutea, where they 

 are almost wholly wanting. In this expansion 

 the fibres are associated into compressed bun- 

 dles, Y^UU to J-QW of an inch wide, either anas- 

 tomosing with each other at very acute angles, 

 or lying parallel for considerable distances. It 



Jrcr,! iTo 6 ^ is ii f an inch thick at the b ttom f ^ ^ 



nerve, of various sizes, and and, gradually decreasing, only g^Vo near tae 



varicose. At a the axis- * . TT ^i 



fibre projects beyond the ora *#ta* or anterior termination. How these 

 meduiia at a broken extre- fibres terminate, is still unknown. (Fig. 295, 1.) 



mity. (Magnified 320 dia- m , . , . . , ' 



meter8-) The expansion of the optic nerve just de- 



scribed by no means constitutes the retina, how- 

 ever. The latter consists of five distinct layers, of which this expan- 

 sion constitutes one. These are from within outwards. (Fig. 295.) 



Fig. 295. 



m 



/ 



3W^p|w^ a|>5 



'^^^^^P^^i^^^r^iM^ % l 



-iiiiiSif^ 



Vertical section of human retina and hyaloid membrane, h'. Nuclei on inner surface of latter, h. 

 Limitary membrane, c. Layer of transparent (epithelial?) cells, c'. Separate cell, enlarged by 

 action of water, n. Gray nervous layer, with its capillaries. 1. Fibrous layer (optic nerve). 2. 

 Gray vesicular layer. 1'. Shred of fibrous lamina, detached. 2'. Cell and nucleus, detached, g. 

 Granular layer. 3. Light lamina, frequently seen, g' . Detached nucleated particle of granular 

 layer. TO. Jacobson's membrane. TO'. Its bacilli, detached, m". Its outer surface. (Magnified 320 

 diameters.) 



1. The limitary membrane. 



2. The expansion of the optic nerve. 



3. The layer of gray nerve-substance. 



4. The granular layer. 



5. The bacillar layer (rods and cones). 



