1526 A MANUAL OF ANATOMY 



Each of these breaks up into two branches, nasal or internal, and 

 temporal or external. The temporal branches keep clear of the 

 macula lutea, but furnish small twigs to it, which, however, do not 

 enter the fovea centralis, this part being non-vascular. As the 

 branches pass inwards and outwards, respectively, towards the 

 periphery of the retina, they ramify freely, and ultimately terminate 

 in capillary networks. The arteries do not extend farther outwards 

 than the inner nuclear layer. No anastomoses take place between 

 the branches of the arteria centralis retinae. 



In the foetus the arteria centralis retinae furnishes a branch to 

 the posterior part of the capsule of the crystalline lens, which 

 reaches it through the canal of Stilling in the vitreous body. 



The veins are ultimately collected into two vessels, upper and 

 lower, which pass through the optic disc, one above, and the other 

 below, the artery. They then form one vessel which opens into the 

 superior ophthalmic vein. The veins of the retina are destitute of 

 muscular tissue, the wall of each being formed by a single layer 

 of endothelial cells, external to which there is a perivascular 

 lymph-space, this, in turn, being limited by another layer of endo- 

 thelial cells. These lymph-spaces are in communication with those 

 of the optic nerve. 



Relation of the retinal layers to one another. — ^The only two 

 layers which are in direct continuity are the stratum opticum and 

 ganglionic layer, some fibres of the former being the axons of the 

 cells of the latter. As regards most of the strata, the constituent 

 elements of successive layers are brought into communication by 

 means of the interlacements which take place between the arboriza- 

 tions formed by their various processes. These interlacements 

 occur in the inner and outer molecular layers. 



In the inner molecular layer there are several strata of interlace- 

 ments, by means of which the dendrites of the cells of the ganglionic 

 layer are brought into communication with the internal processes 

 of the bipolar cells of the inner nuclear layer. In the outer mole- 

 cular layer there is a free intermingling between the external pro- 

 cesses of the bipolar cells of the inner nuclear layer and the rod- 

 fibres and cone-fibres. 



Nerve-cells of the Retina. — These are arranged in three strata, 

 and are in communication with one another through interlacing 

 arborizations. The outermost stratum consists of the rods and 

 cones ; the middle stratum is formed by the bipolar cells ; and the 

 innermost stratum represents the cells of the ganglionic layer. 

 The axons of the ganglionic cells enter the stratum opticum as 

 centripetal fibres, which pass in the optic nerve to the brain. The 

 centrifugal fibres of the stratum opticum ramify in the inner 

 molecular or inner nuclear layer. 



