OEGANS OF SENSE. 



is made up entirely by these external enlargements 

 or granules, the second to the internal granular layer, 

 and the third series of enlargements is intimately 

 mingled with the fibres of the optic nerve, and with 

 them constitutes the fibrous stratum of the retina. 

 The external and middle enlargement of the fibres of 

 Miiller are composed of cells ; the internal enlarge- 

 ment consists of a homogeneous mass, with a depres- 

 sion upon its inner surface, by which it rests upon a 

 very delicate structureless lamella (2 oVo-th of a line in 

 thickness) which constitutes the limitary membrane 

 of the retina within. 



On the internal surface of the internal granular 

 layer, and consequently between it and the fibrous 

 layer, is a stratum composed of multipolar or caudate 

 nerve cells (nervous layer) ; and the fibrous layer, as 

 already stated, consists of an expansion of the fibres 

 of the optic nerve.* These latter, as they run for- 

 wards towards the anterior border of the retina, 

 curve outwards to unite themselves with the pro- 

 longations of the nerve-cells, which, in their turn, 

 send an anastomosing fibre to each of the middle 

 enlargements on the fibres of Miiller. In the centre 

 of the yellow spot of Scenamering we find nothing but 

 nerve-cells within the meinbrana Jacobi. 



In reviewing what has just been said in relation to 

 the arrangement of the diverse elements composing 

 the retina, it is obvious that this membrane presents 



* The superposition of a layer of nerve cells upon a layer of nerve 

 fibres recalls the structure of the convolutions of the cerebrum and cere- 

 bellum. The capillary layer of the retina formed by the branches of the 

 arteria centralis retinae occupies the stratum of nerve cells. (Ed.) j 



