364 NORMAL HISTOLOGY. 



hyaloid is reflected, its surface is marked by radiating folds, which 

 at the edge of the ciliary processes become converted into the stiff 

 fibres distinguishing the free part of the zonula. These fibres form 

 two series, the one comprising the fibres springing from the sum- 

 mit of the ciliary processes, the other consisting of those fibres 

 which take their origin in the depressions between the ciliary pro- 

 cesses ; the fibres extending from the valleys pass to the anterior 

 surface of the lens, where they blend with the outer lamella of the 

 anterior capsule, while those springing from the summits of the 

 processes are inserted into the periphery and the immediately ad- 

 joining parts of the posterior capsule. 



The narrow annular cleft, triangular in section, bounded in front 

 by the zone of Zinn, mesially by the lens, and behind by the mem- 

 brane of the vitreous body, constitutes the canal of Petit. Owing 

 to the constrictions produced by the shorter bridging fibres, the canal 

 presents a series of alternate constrictions and dilatations, 

 which, on inflation, map out the position of the canal by a ring of 

 bead-like enlargements. 



THE VITREOUS BODY. 



The vitreous body occupies the space between the lens in front 

 and the retina behind ; it consists of the vitreous substance en- 

 closed by the glassy hyaloid membrane, which in front, where it 

 supports the lens within the patellar fossa on its anterior surface, 

 comes in direct contact with the posterior capsule. 



The substance of the vitreous body is remarkable, in addition 

 to its beautiful transparency, for its great fluidity, consisting of 98.6 

 per cent, of water, the remaining small portion being made up of 

 solids, including its organized parts. Histologically, the adult vitreous 

 substance corresponds to connective tissue containing an enormous 

 watery infiltration whose fixed elements have undergone degener- 

 ation. In its embryonal condition the vitreous body is composed 

 of delicate gelatinous or mucoid mesodermic tissue containing 

 numerous frail stellate cells. 



The formed elements of the vitreous are of two kinds, fibres 

 and cells. The fibrous elements occur in the superficial part of 

 the vitreous, in the vicinity of the ora serrata, as fibrillse of extreme 

 delicacy, which take part in the formation of the zone of Zinn. 

 Other fibrous structures are present as the remains of the minute 

 blood-vessels permeating the vitreous in its embryonal condition. 



The cells of the vitreous body belong to the category of wan- 

 dering corpuscles or leucocytes, the fixed connective-tissue cells 

 being wanting in the matured organ. 



In the central part of the vitreous body, the central or hyaloid 



