730 THE EYE. 



like appearance. Only capillary vessels occupy the yellow spot, the larger 

 branches passing round it. 



Fig. 479. 



Fig. 479. VERTICAL SECTION OP THE RETINA THROUGH THE MIDDLE OP THE FOVEA 

 CENTRALIS (from Henle.) ~- 



This figure is taken from a preparation of the human retina hardened in alcohol, and 

 is designed to show the peculiarities of this part as compared with other regions of the 

 retina, viz., the obliquity of the Miillerian fibres, the thinness of the layer of nerve- 

 fibres, and the absence of the granular layer in the centre, a, 6, cones of the columnar 

 layer ; c, external nuclear layer ; d, internal nuclear layer ; /, external fibrous layer ; 

 g, molecular substance next to h, the ganglionic layer ; Tc, the layer of nerve-fibres ; 

 I, the internal limiting membrane. 



The yellow colour of the macula lutea is deepest towards the centre, and 

 is due to a pigment which imbues all the layers except the columnar : it 

 does not appear to be contained in cells, and is soon removed after death by 

 the action of water. 



Ciliary part of the retina. The structure which has been named the 

 ciliary part of the retina is situated in front of the ora serrata, and extends 

 thence over the inner ends of the ciliary processes to the base of the iris 

 (therefore, over the whole corona ciliaris). Though entirely destitute of the 

 nervous parts of the retinal structure, it is still in continuity with the sub- 

 stance of the retina, and in the form of a grey membrane, adheres to the 

 ciliary processes and zonule of Zinn, and is usually in great part detached 

 from the neighbouring parts along with the latter. According to Kolliker, 

 this layer consists of elongated nucleated cells, which in the human subject 

 are broad externally, and with flat or forked bases set upon the internal 

 limiting membrane. He regards these cells as probably corresponding to the 

 Miillerian fibres, and as constituting in this place the only representative of 

 the retinal structure. 



