ORA SERRATA AND PARS CILIARIS. 289 



have undergone such diminution in the vicinity of the ora 

 serrata, that their united thickness only amounts to 012 to 

 014 of a millimeter. The nerve and ganglionic spheroids become 

 very sparingly scattered, so that they can only be found quite 

 isolated between the internal extremities of the radial fibres ; 

 the granular layer, in consequence of the preponderating 

 amount of the latter, has likewise become more vertically 

 striated, so that ultimately its inner boundary disappears. The 

 internal granule layer consists of only two or three not very 

 closely arranged tiers of granules, and not unfrequently simple 

 nuclei appear to occupy their place in the fibrous mass which 

 extends through the slender intergranule layer to the external 

 granules. The rods and cones are distinct, though they have 

 become somewhat shorter. Just before the point of greatest 

 attenuation, the retinal layers severally lose their peculiar 

 characters to a still greater degree, and pass into an obscurely 

 vertically striated mass, in which numerous roundish or oval 

 nuclei are distributed. The bacillar layer is alone excepted 

 from this general fusion or indifference of tissue, remaining 

 to the last a separate layer, the elements of which rapidly 

 diminish in size, and finally cease. As soon as this takes place 

 the remaining layers form a single tier of cells, which con- 

 stitutes the pars ciliaris, and is the immediate prolongation of 

 the retina proper. The ''cells resemble in general those of 

 columnar epithelium, but vary in height in different animals. 

 H. M tiller examined this region, particularly in the Pig, Ox, 

 Rabbit, Pigeon, and Fowl. In the Rabbit their height amounts 

 to 0'025 of a millimeter." H. Miiller regards these cells as a 

 continuation of the indifferent supporting apparatus of the 

 retina, " whence, as it appears, the inner extremities of the 

 radial fibres are perhaps to be reckoned as belonging to 

 such of the inner granules as correspond to the in most 

 animals distinctly different nucleated radial fibres . . ." More- 

 over the form of the cells in question is in some parts in Man such 

 as to render their epithelial nature doubtful. They are isolated, 

 frequently not rounded at the extremities, but provided with 

 one or with several dentations and short processes, which are 

 given off also from the longer side, so that they might be 

 considered to belong to the group of connective tissues, against 

 VOL. III. 



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