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VETERINARY PHYSIOLOGY 



layer (6) of the retina, and they pass backwards and end in 

 two special kinds of terminations in the seventh layer of the 

 retina — the rods and cones (7). These structures are com- 

 posed of two segments — a somewhat barrel-shaped basal 

 piece, and a transparent terminal part which in the rods 

 is cylindrical and in the cones is pointed. Over the central 



Fig. 64. — The use of the Ophthalmoscope, A, by the direct method. B, 

 by the indirect method. E, eye observed. E'^, observer's eye. M, 

 mirror. S, source of light. L, convex lens. The direction of the 

 ingoing rays is shown in strong lines, of the rays from the observed 

 eye in thin lines. 



spot of the eye there are no rods, but the cones lie side 

 by side, and the other layers of the retina are thinned out. 

 The rods and cones are imbedded in the last or eighth layer 

 of the retina — the layer of pigment cells, or tapetuni nigrum. 

 The retina stops abruptly in front at the ora serrata, but the 

 tapetum nigrum, along with another layer of epithelial cells 

 representing the rest of the retinal structures, is continued 



