360 MICROSCOPIC ANATOMY OF THE ORGANS. 



(9) The Nerves of the Eyeball. 



The nerves which, in addition to the optic nerve, terminate 

 in the eyeball penetrate the sclera in the region of the optic 

 nerve, and run forward in the suprachorioidea. On their way 

 they give off branches to the chorioidea, and form on the outer 

 surface of the ciliary muscle a plexus which contains numerous 

 groups of ganglion cells (plexus gangliosus ciliaris). From 

 this, small branches run to the ciliary body, the iris, and the 

 cornea. 



The nerves to the ciliary body end in the walls of the 

 blood-vessels, in the ciliary muscle, and in the lamina supra- 

 chorioidea, in the form of extremely fine end arborizations. 



The nerves to the iris form an annular plexus in the iris 

 stroma. They lose their medullary sheaths and supply the 

 smooth muscle and the vessels of the iris, and form a fine 

 plexus on its anterior surface. 



The nerves to the cornea form a network in the sclera 

 around the corneal border the plexus annular is, from which 

 branches proceed to the cornea and conjunctiva. The corneal 

 branches enter from the sclera into the substantia propria of 

 the cornea, where they lose their medullary sheaths and form 

 plexuses at different levels. Of these, we distinguish four : 



(a) The ground plexus, in the deeper layers of the sub- 

 stantia propria; 



(b) The subbasal plexus, just under the lamina elastica an- 

 terior ; 



(c) The subepithelial plexus, in the deeper layers of epi- 

 thelium ; and 



(d) The intr a- epithelial plexus. The last plexus is made 

 up of fine fibres running between the epithelial ceils to the 

 outermost layers, where they end freely in knob-like swellings. 



According to Dogiel, some of the nerves in the substantia 

 propria corneae terminate by means of end plates. Some, on 

 the other hand, end at the edge of the cornea in terminal 

 bulbs (Krause), which are to be found also in great numbers 

 in the conjunctiva. 



