1108 



granules at their point of junction. In the centre of the vitreous humor, running 

 from the entrance of the optic nerve to the posterior surface of the lens, is a canal, 

 filled with fluid and lined by a prolongation of the hyaloid membrane. This is 

 the hyaloid canal (canalis hyaloideus) (Fig. 797), which in the embryonic vitreous 

 humor conveyed the minute vessel from the central artery of the retina to the back 

 of the lens. 



The hyaloid membrane encloses the whole of the vitreous humor. Tn front of 

 thp ora serrata it is thickened by the accession of radial fibres and is termed the 

 zonule. of Zinn (zonula ciliaris} (Figs. 816 and 820). Here it presents a series of 

 radially arranged furrows, in which the ciliary processes are accommodated and to 

 which they are adherent, as evidenced by the fact that when removed some of their 

 pigment remains attached to the zonule. The zonule of Zinn splits into two 



ZONULA CILIARIS, 



(Zinni) 



ORBICULAR!* 



CILIARIS 



CHORIOIDEA 



FIG. 816. The zonule of Zinn or the suspensory ligament of the lens viewed from behind in connection with 



the lens and the ciliary body. (Toldt.) 



layers, one of which is thin and lines the fossa h yaloidea ; the other is named the 

 suspensory ligament of the lens; it is thicker, and passes over the ciliary body to be 

 attached to the capsule of the lens a short distance in front of its equator. Scattered 

 and delicate fibres are also attached to the region of the equator itself. This 

 ligament retains the lens in position, and is relaxed by the contraction of the radial 

 fibres of the Ciliary muscle, so that the lens is allowed to become more convex. 

 Behind the suspensory ligament there is a sacculated canal, the canal of Petit 

 (spatia zomdaria), which encircles the margin of the lens and which can be easily 

 inflated through a fine blowpipe inserted through the suspensory ligament. It 

 is bounded in front by the anterior layer of the suspensory ligament of the lens, 

 behind by the membrana hyaloidea, and internally by the capsule of the lens. 

 The canal of Petit is a lymph space. All of the spaces of the canal of Petit com- 

 municate with the posterior chamber of the eye. 



No vessels penetrate the vitreous body, although a lymph channel remains; 

 so that its nutrition must be carried on by the vessels of the retina and ciliary 

 processes, situated upon its exterior. 



in. The Crystalline Lens (Lens Crystallina) (Figs. 817, 818). 



The crystalline lens, enclosed in its capsule, is situated immediately behind the 

 pupil, in front of the vitreous body, and is encircled by the ciliary processes, which 

 slightly overlap its margin. 



