EXAMIXATIOX OF THE EYEBALL 



849 



the only retinal layer re])resented, and where consequently tlie retina is extremclv 

 thin. The nerve-tiljres run on the inner surface of the retina and are continuous 

 with those of the optic nerve; they constitute the only retinal layer that is con- 

 tinued into the intraocular end of the nerve. The nerve-cells are found l^etween 

 these surface layers. The larger hlood-vessels of the retina run in the inner layers, 

 and none encroach on the layer of nerve-epithelium. 



Within the coats mentioned, the interior of the eyeball is fully occupied by con- 

 tents, which are divided into three parts, and differently named according to their 

 consistence and anatomical form. They are all transparent, as through them the 

 light has to pass so as to gain the retina. Of these the only one that is shari)ly and 

 independently outlined is the lens, which is situated in the anterior half of the'glol)e 

 at the level of the ciliary processes, where it is suspended between the other con- 

 tents, which fill respectively the space in front of it and the space behind it. The 



Fig. 477. — Semi-diaorammatio Horizontal Pkctiox TiiRoroii Eyeball and Optic 

 Nekve. (Alter Elfinger. Keduced and altered.) 



Corneal epithelium 

 CORNEA 



; ,y X "^ 



CANAL OF SCHLEWy 



Ciliary muscle 



,^^^e5^^^^^-V^ LENS v^^^*^'*'^»^^\ 



CANAL OF PET;T 



RETL\A 



Central retinal vessel- 

 OPTIC NERV E- 

 SUBSTASCI: 

 PIAL NERVE- 

 SHEA TH 



SCLEROTIC 



[covered eiler- 

 iiallyby Tenon's 

 capsule anil 

 loose tisstm) 



D IRA L yER \ -E-SHEA TH 



space in front is called the anterior or aqueous chamber; that behind the lens is tbe 

 vitreous chamber. 



The lens is a biconvex V)ody.with its surfaces directed anteriorly and posteriorly: 

 these surfaces meet at its rounded-oft' edge or equator, which is near (but does not 

 touch) the ciliary processes all round. The posterior is considerably mori" convex 

 than the anterior surface; the central part of each surface is called its pole. The 

 lens is closely encased in a hyaline elastic capsule, thicker over the anterior than 

 over the posterior surface. Thus enclosed, it is held in position in the globe by a 

 suspensory ligament, attached to its capsule near the ecjuator all round, and swung 

 from the ciliary region. Posteriorly, the lens rests in a cup formed ]»y tbe front jtart 

 of the vitreous, while its anterior capsule is in contact with the aqueous fluid and 

 lies close against the back of tbe pujiillarv l)order of tbe iris, ^^'ben in j)osition 

 the lens measures nine millimetres across, and about four milHmetres between its 

 poles. On eacb surface a series of fine, sinuous, grey lines can Ix^ seen radiating 

 from the pole towards the equator, called respectivelv tb*- anterior and posterior 

 54 



