OPTIC NERVE 



861 



nerve loosely as its outer or dural sheath. The nerve is elosely enveloped l.y 

 a vascular coverinjf derived from the pia mater, named aecordingly the pial 

 sheath. The space between these two sheaths, known as the inter rafjinal x^xirc, 

 is subdivided hyaline prolongation of the arachnoid (the arachnoidal sheath j into 

 two parts, viz. an outer, narrow, aabdaral, and an inner, wider, .■oilxinirhndld 



Fio. 487. — Transverse Section thuolgii Optic Nerve, showing the Relations of 

 ITS Sheaths and Connective Tissue Framework. 



SUBARACHNOID SPACF 



SUBDURAL SPACE 



DURAL SHEATH 

 ARACHNOIDAL SHEATH 



Central retinal artery 

 Central retinal vein 



Conneetive-tisBue frame- 

 work, with meshes in 

 which the nerve-flbre 

 bundles lie 



space, communicating with the corresponding intracranial spaces. The arachnoidal 

 sheath is connected with the sheath on each side of it by numerous fine processes 

 which bridge across the intervening spaces. The pial sheath sends processes 

 iuAvards, which form a framework separating the bunclles of nerve-libres ; between 

 the enclosed nerve-tiljres and each mesh of this framework there is a narrow interval 



Fig. 488.— Longitudinal Section through Termination of Optic Nerve. 



physiological pit 



RETINA 



PIGMENT EPITHELIUM 



OURAL SHEATH 

 PIAL SHEATH 



ARACHNOIDAL SHEATH 



OPTir XERl'E 

 n/T/f ITS 

 COSSKCTIVE- 

 TISSVE 

 FRAMEWORK 



SJf?i— SUPRACHOROIDAL 

 '*T%" SPACE 



-2^- LAMINA CRIBROSA 



"' SCLEROTIC 



occupied l>y lymph. The nerve-filtres are medullated. but have no primitive sheath. 

 About fifteen or twenty millimetres l)ehind the globe the central vessels enter, 

 piercing ol)liquely the lower outer (|uadrant of the nerve, and then run forward 

 in its axis. They are accom])anied throughout by a special process of tin- j'ial 

 sheath, which forms a fibrous cord in the centre of the nerve. 



