NERVOUS CONSTITUENTS OF THE RETINA. 237 



substance of tolerably equable thickness in Man, amounting to 

 about ten micro-mill, through the whole retina. In the finely 

 striated matrix of the connective tissue, extraordinarily fine 

 fibrils are imbedded, which run without branching for consider- 

 able distances, either obliquely or parallel to the surface of the 

 retina, and are to be regarded, like the similar ones of the internal 

 granule layer, as nerve fibres, on account of the fine fusiform 

 varicosities they present, and their otherwise smooth surfaces. 

 These fibres are in part developed from the peripheric processes 

 of the internal granules, and in part from the fibres of the rods 

 and cones. Isolated nuclei are scattered generally in this layer, 

 but probably all belong to the connective tissue, which at this 

 spot presents many modifications in different animals that 

 will be hereafter described. We possess no more information 

 of the nervous fibres of this layer than of those of the internal 

 granule layer. Their course deviates from the radial ; and 

 although, in occasional instances, fibres may be seen passing 

 straight through it,* the greater number appear to form a 

 fine plexus in the plane of the retina, so fine and complex, 

 indeed, as to be equalled only by the grey substance of the 

 central organs. 



TJte rod and cone fibres, which form an essential constituent 

 of the external granule layer, are rooted by their inner ends in 

 the external granulated layer. All the so-called external gra- 

 nules are nucleated swellings of these fibres. The layer of the 

 rods and cones is immediately superimposed upon the external 

 granules, owing to the above-named fibres being in direct 

 continuity with the latter. A sharp contour- line which in 

 transverse sections of the retina divides the external granules 

 from the rods and con;s, constitutes the external limiting 

 membrane. 



In most parts of the retina of Man, and almost everywhere 

 in animals, the space intervening between the limitans externa 

 and the external granulated layer is not larger than is necessary 

 for the disposition of the external granules (a single nucleus 

 corresponding to each rod and cone) and the fibres belonging to 

 them, putting aside the small quantity of connective tissue which 



* Hasse, Zeitschrift fur rat. Medicin, Band xxix., p. 255. 



