3 6 4 



HISTOLOGY. 



ately in front of the ora serrata enter the vitreous body, but a much larger 

 number pass between the ciliary processes to the lens. They are attached 

 to the borders of its capsule, overlapping slightly its anterior and posterior 

 surfaces. Thus they form the zonula ciliaris [suspensory ligament] 

 which holds the lens in place (Fig. 410). The zonula is not a continuous 

 layer, nor does it consist of two laminae, one to the anterior and the other 

 to the posterior surface of the lens with a space between them. It con- 

 sists rather of numerous bundles, between which and the vitreous body, 

 and among the bundles themselves, there are zonular spaces [canals of Petit] 

 which communicate with the posterior chamber. 



OPTIC NERVE. 



In its intraorbital portion the optic nerve is surrounded by prolonga- 

 tions of the meninges. On the outside is the dural sheath, consisting of 



Central artery. 

 Fibers of the lamina cribrosa. | Central vein. 



Hyaloid membrane 

 loosened. 



Retina. 

 .Chorioid. -f - 



Sclera. - 



Bundles of the optic nerve. - 

 Pial sheath. 



Arachnoidal sheath. 



Dural sheath. 



FIG. 416. LONGITUDINAL SECTION OP THE OPTIC ENTRANCE OF A HUMAN EYE. X 15. 

 Above the lamina cribrosa is seen the narrowing of the optic nerve, due to its loss of myelin. The central 

 artery and vein have been for the most part cut longitudinally, but above at several points trans- 

 versely. 



thick outer longitudinal and inner circular bundles of connective tissue 

 with many elastic fibers. Internally it is connected with the arachnoid 

 layer by few dense strands of tissue, and the arachnoid joins the pial sheath 

 by many branched trabeculae. .The pia surrounds the entire nerve and 

 sends anastomosing layers among the bundles of nerve fibers. The latter 

 are slender and medullated but without a neurolemma; they are supported 

 by long-rayed neuroglia cells which extend between the individual fibers, 

 but are most numerous at the periphery of the bundles and of the entire 



