THE RETINA. 



203 



FIG. ioo. 



Optic Disc or Papilla, the point where the optic nerve enters, the central 

 artery of the retina piercing its centre. It lies about -^ inch internal to 

 and -jL- inch below the posterior pole of the eye, and is often called the 

 Blind Spot, being the only part of the fundus oculi from which the power 

 of vision is absent. 



Pars Ciliaris Retina, the part of the retinal stroma which is prolonged 

 over the ciliary body. It is destitute of nerve-elements. 



Arteries of the Retina, arise from the Arteria Centralis Retinoe (br. of the 

 ophthalmic), just behind the optic disc; run chiefly upwards and down- 

 wards, accompanied by veins, to terminate in capillary network. No 

 vessels exist in the fovea centralis, and only the finest capillaries in the 

 macula lutea. 



Describe the Structure of the Retina. It 

 is composed of nervous elements, blood-vessels, 

 and modified connective tissue resembling the 

 neuroglia of the brain, arranged in 9 or IO 

 layers, from within outwards, as follows, viz. 



Membrana Limitans Interna, a perfectly 

 transparent membrane, made up of the 

 retinal connective tissue, and lining the 

 inner surface of the retina (shown in the 

 cut by the lowest line). 



Optic Nerve Fibres,' 1 composed of the ter- 

 minal fibres of the optic nerve radiating 

 from the papilla in all directions. They 

 consist of the axis-cylinder only. 



Ganglionic Layer? a very thin layer of 

 large ganglion cells, having large nuclei 

 and nucleoli, with branching processes to 

 the optic nerve fibres of next layer. 



Internal Molecular Layer,* fine granules 

 intersected by finest nerve fibres and con- 

 nective tissue elements. 



Internal Granular Layer,** small, round 

 cells with large nuclei, their processes 

 uniting with the ganglion cells. 



External Molecular Layer, 5 a very thin 

 layer of fine granules and nerve-fibrillse. 



External Granular Layer,* consists of 

 ellipsoid cells, forming a nucleated en- 

 largement of Jacob's membrane. 



