Observations on tlie structure of the central fovea of tlie liumaii eye. 19 



this is a point which we have not found noticed by any previous ob- 

 server^). Kuhnt indeed goes so far as to describe the most central 

 fibres as immediately diverging from their nuclei in an almost hori- 

 zontal manner, and Hulke and M. Schultze (in one section) also depict 

 them as at once diverging to either side. This also we are quite 

 unable to understand unless there is a vast difference of structure in 

 diff'erent foveae. 



7. As to the form, sue, and appearance of the cone-nuclei in 

 the fovea. 



In our chromic acid specimens the cone-nuclei throughout all parts 

 of the retina are nearly spherieal and diifer in this point from the 

 rod-nuclei, which are somewhat oval in form. They all have a di- 

 stinct nucleolus and punctated appearance, apparently due to a 

 network. At the edge of the fovea they have a diameter of about 

 0-0071 mm., while the rod-nuclei measure 0-0057 mm. in length but 

 only about 0*0043 mm. in breadth. The nuclei belonging to the 

 most central cones are smaller than the others, the diminution however 

 not occurring abruptly; those at the very centre only measure about 

 0-0057 mm., that is to say about the same as the length of the rod- 

 nuclei at the edge of the fovea. They are interpolated at different 

 levels in adjacent fibres, no doubt for convenience of packing; here 

 and there one is seen at an entii^ely different level from the rest. 

 They have usually been represented as oval in this part of the retina 

 but Krause has given their spherical shape and general appearance 

 fairly accurately. 



8. As to the inner granule layer (layer of hipolars) and the 

 molecular layers at the fovea. 



The layer of inner granules becomes gradually reduced in size 

 and in the number of its constituent granules from the edge of the 

 fovea inwards; more rapidly as the middle third is approached so 

 that they soon become not more than two or three and finally not 

 more than one deep. Here they appear to be imbedded in what 

 looks like a blending of the two molecular layers, but since the 



^) Cajal however represents a similar condition of the cone-fibres in the centre 

 of the bird's fovea. La Cellule. T. IX PL VI. Fig. 15. 



9* 



