236 THE RETINA, BY MAX SCHULTZE. 



Man, as amongst the Yertebrata generally, the innermost layer 

 frequently contains somewhat larger granules. Besides these 

 two forms and the nuclei of the supporting fibres, W. Krause* 

 distinguishes a fourth kind of internal granules, which form the 

 outermost layer, and project into the external granulated layer 

 (Krause's membrana fenestrata). These he believes are unipolar, 

 and have no connection with the outer layers of the retina,f but 

 form the terminal organs of the optic fibres. 



A structural difference exists in some animals, especially 

 amongst Fishes, in regard to the cells projecting into the inner 

 granule layer, which unite with the layer I have termed the 

 fenestrated intergranule layer (stratum intergranulosum fenes- 

 tratum).^ I consider these to be formed by a special develop- 

 ment of the connective tissue of the next layer. 



The thickness of the internal granule layer in Man amounts, 

 according to H. Miiller, to 0*03 or 0'04 of a millimeter, dimi- 

 nishing towards the ora serrata, where, at most, three tiers of 

 granules lie superimposed upon one another, to O02 of a milli- 

 meter, but increasing at the yellow spot to about 0'06 of a 

 millimeter. 



The layer of internal granules is separated from the layer 

 of external granules by an intergranule layer, which consists 

 of a thin layer of fine plexiform tissue enclosing a few nuclei 

 and smooth cells, with coarser fibres running parallel to the 

 surface of the retina, which are capable of being raised in the 

 form of thin laminye. In Man and the higher Vertebrata this 

 appears in sections of the retina as a finely punctated granular 

 layer, which, though much thinner, presents a very close 

 resemblance to the internal granulated layer. On this account 

 Henle designated it the external granulated layer, a term that, 

 as already stated (p. 220), we shall adopt in order to avoid con- 

 fusion with H. Muller's intergranule layer. W. Krause has re- 

 cently employed the term membrana fenestrata to indicate it. 



The external granule layer, in its simplest form, as seen 

 in Man and Mammals, consists of a thin layer of granulated 



* Membrana fenestrata, p. 42. 



t See W. Krause's Schema, loc. cit. , Taf . ii. , fig. 21, gri. 



$ De Retime structura, 1859, p. 13. 



