246 



THE KETINA, BY MAX SCHULTZE. 



ated in the posterior part of the fundus, at about the middle of 

 their length. I estimate the length of each segment in this 

 region at about twenty-five or twenty-seven mieromillimeters. 

 The boundary line between the external and the internal segment 

 of adjoining rods lies, for the most part, in one and the same 

 plane. The plane of junction of the two segments in the cones, 

 however, is different, being situated more anteriorly both in Man 

 and Mammals. The inner segment of the cones (the body of the 



Fig. 352. 



Fig. 352. Cones and rods, 9 ; limitans externa, 8 ; and part of tlie 

 external granule layer, 7 ; from the posterior part of the retina of the 

 Pig. Each of the cones, which are in very close apposition, contains 

 in its inner segment a highly refractile body, the function of which is 

 unknown. Magnified 800 diameters. 



cone) is consequently always shorter than that of the adjoining 

 rods; the difference in length between the inner segments of 

 the rods and of the cones at the posterior part of the eye 

 amounting in Man, upon the average, to six mieromillimeters. 

 On account of the great difficulties encountered in obtaining a 

 view of the fresh and uninjured cones, it is by no means easy 

 to ascertain their exact length. It appears, however, to be the 

 rule that where rods and cones occur mingled together, the 

 outer segments of the cones are always shorter than those of 

 the rods. In Man I estimate the length of the conical outer 



