Chap, xxxix.] THE RETINA. 317 



proper. In this the rods and cones, with their fibres 

 and the nuclei of the outer nuclear layer, corre- 

 spond to columnar epithelial cells (the sensory epithe- 

 lium), while all the other layers i.e., the outer mole- 

 cular, inner nuclear, inner molecular layer, ganglion 

 cells, nerve-fibres, and limitans interna represent 

 Briicke's tunica nervea or Henle's stratum nerveum. 



449. The blood-vessels of the retina. The 

 branches of the arteria and vena centralis of the optic 

 nerve can be traced into the retina in the layer of 

 nerve-fibres and ganglion-cells, while the capillaries 

 connecting the arteries with the veins extend through 

 the layers up to the outer molecular layer. 



The lymphatics of the retina exist as perivascular 

 lymphatics of the retinal veins and capillaries (His). 

 Lymph channels are present in the nerve-fibre layer. 



450. The lamina cribrosa is the part of the 

 sclerotic and choroid membrane through which the optic 

 nerve-fibres have to pass in order to reach the papilla 

 nervi optici. In the optic nerve the fibres are grouped 

 in larger or smaller groups not bundles, in the sense 

 of those present in other nerves and surrounded by 

 perineurium (see a former chapter) but surrounded 

 by septa of connective tissue, and these groups pass 

 through corresponding holes of the sclerotic and choroid. 



451. The optic nerve possesses three sheaths, 

 composed of fibrous connective tissue (a) an outer, 

 or the dural ; (b) a middle, or arachnoidal ; and (c) an 

 inner, or pial, sheath which are continuations of the 

 respective membranes of the brain. The pial sheath 

 is, in reality, the perineurium, the whole optic nerve 

 being comparable to a compound nerve-bundle as de- 

 scribed in a former chapter. The dural sheath of the 

 optic nerve, at its entrance into the lamina cribrosa, 

 passes into the outer strata of the sclerotic, while the 

 arachnoidal and pial sheaths pass into the inner strata 

 of the sclerotic. Outside the dural sheath is a lymph 



