CII. LVI.1 



THE HODS AND CONES 



773 



6. OiLtc,r motoufar /*/<'/: This layer closely resembles the inner 

 molecular layer, hut is much thinner. It contains the branchings of 

 the nd and cone fibres on the 



one hand an<l of the bipolar 

 (Us on UK; other. 



7. External nuclear layer. 

 This layer consists of small cells 

 resembling at, first sight those 

 !' tin- internal nuclear layer; 

 they are classed as rod and cone 

 granules, according as they are 

 eonnerted with the rods and 

 eones respectively, and will be 

 described with them. They are 

 lodged in the meshes of a frame- 

 work, which is formed by the 

 breaking up of the M iilierian 

 fibres. 



8. Membrana limitans externa. 

 This is a well-defined mem- 

 brane, marking the internal 

 limit of the rod and cone layer, 

 and made up of the junction 

 of the sustentacular fibres ex- 

 ternally. 



!). Lat/iir of rods and cones. 

 This layer is the nerve-epithe- 

 lium of the retina. It consists 

 f two kinds of cells, rods and 

 cones, which are arranged at 

 right angles to the external limit- 

 ing membrane, and supported by 

 hairlike processes (basket) proceeding from the latter for a short 

 distance (fig. 572). 



Kach rod (fig. 573) is made up of two parts, very different in 

 structure, called the outer and inner limbs. The outer limb of the 

 rods is about 30//. long and 2/m broad, is transparent, and doubly 

 refracting. It is said to be made up of fine superimposed discs. 

 It stains brown with osmie. add but not with haematoxylin, and 

 resembles in Home ways the myelin sheath of a medullated nerve. 

 It is the part of the rod in \\hich the pigment called visit al purple is 

 found. In some animals, a few rods have a greenish pigment instead. 

 The inner limb is about as long but slightly broader than the outer, 

 is longitudinally striated at its outer and granular at its inner part. 

 It stains with ha-matoxylin, but not with osmic acid. Each rod is 



Km. fi78. Diagram show inn Hit) IHTMU 

 it' ii-tina. |, Ni-i \i--hlint of ganglion roll; _', pro- 

 cesses of ganglion cHl -null' tuit.uards ; H, nerve- 

 lil'ir passing from bipolar cell in inner nur!<>:ir 

 layer; -I, process of ganglion cell towards liipnl.-ir 

 Mil; !>, arliorisiiUons of liluvs fnnn rods ami 

 DOOM with tin 1 luaiiclirs of lii|Milar I'flla. 



(1-V.nii M'K.'inlri.'k, uft.rHt.ilir.) 



