HEAD AND NECK OF THE HORSE 



123 



the papilla is pitted by the excavatio jpapillce nervi O'ptici. It should 



be remembered that the optic papilla, having no nerve elements except 



nerve fibres, is the " blind spot." Thirty or forty small arteries, branches 



of the central artery of the retina, with their satellite veins, radiate from 



the papilla. 



Dissection. — To obtain the isolated vitreous body and crystalline lens, 

 the method suggested by Anderson Stuart should be followed. An eye- 

 ball is allowed to lie untouched for some time — one to three days, accord- 

 ing to the season. An incision is then made along the equator through 

 the three tunics, and the two Halves of the eyeball are gently separated. 

 If this is properly done, the vitreous body and lens may be allowed to 

 drop entire into water, or, still better, into a stain in which they may 

 remain for some nnnutes. If stained, the specimen should be well washed 

 before examination. 



Vessels of iris 



Vessels of ciliary processes. 



Chorio-capillaris. 



Corneal loop 



Circulus iridis 

 major. 



Sinus venosus 

 sclerse. 



Posterior con 

 junctival vessels 



Central vessels 



of the retina. 



Vessels of inner 

 sheath of optic 

 -nerve. 



Vessels of outer 

 . sheath of optic 

 f nerve. 



w 



1 I Short posterior 

 ciliary arteries, 

 i Short posterior 

 I ciliary vein. 

 Long posterior ciliary artery. 



I I 



Recurrent artery of choroid. ! Vorticose vein. Episcleral vessels. 

 Anterior ciliary vessels. 



Fig. 53. — Diagram of the vessels of the eyeball. (After Leber, moditied.) 

 The vitreous hody^ (corpus vitreum) is a transparent, jelly-like 

 substance occupying the posterior part of the cavity of the eyeball, and 

 intervening between the crystalline lens and the retina. In front, 

 adaptation to the lens produces the hyaloid fossa (fossa hyaloidea). 

 The rest of the surface of the body is convex and applied to the optic 

 and ciliary parts of the retina, but is not in any way connected with 

 this membrane except at the entrance of the optic nerve. 



The surface of the vitreous body is covered by a delicate hyaloid - 

 membrane (membrana hyaloidea), which, over the ciliary body, is 

 thickened by the accession of radial fibres. The thickened part of the 

 membrane is the ciliary zonule (zonula ciliaris), which is firmly 

 adherent to the ciliary processes to which it is adapted by a series of 



1 Vitreus [L.], glassy. 



- i^dXoi (hyalos) [Gr.], glass. 



