32 INNERVATION. [CHAP.XVII. 



to it by an extremely transparent layer of cells, which often remain 

 invisible until swollen by the imbibition of water (fig. 117, c, c'). 

 These cells serve merely as a bond of connexion between the hyaloid 

 membrane and the fibrous lamina of the retina. Between the 

 anterior border of the retina and the border of the lens, the vitreous 

 body is accurately adapted to the ciliary striae and processes of the 

 choroid, and presents a series of plaitings precisely similar to those of 

 the processes themselves, and termed the ciliary processes of the vitre- 

 ous body. Collectively they form a circle called zonula ciliaris, or, 

 zone of Zinn, The two structures are in a manner dovetailed into 

 one another; and so intimate is their union, that, when the processes 

 of the choroid are drawn away from the vitreous body, some of 

 their pigment is generally left adhering to the processes of the 

 latter. 



In the centre of its anterior surface, in a space nearly corresponding 

 to the area between the points of the ciliary processes, the vitreous 



body is hollowed out to receive the crys- 

 Fig ' 12 * talline lens. This latter is contained in, or 



bounded by, a perfectly closed capsule, 

 composed of a tissue exactly resembling the 

 elastic lamina of the cornea already de- 

 scribed. To the whole posterior surface of 

 this capsule, and to a very narrow circum- 

 ferential portion of its anterior surface, 

 the fibrous structure of the vitreous body 



Position of the Lens in the vitreous is firmly attached; the hyaloid mem- 

 humor, shown by an imaginary sec- , i < i i i i 



tion. The dark triangular space on brane itseli not passing behind the lens, 



each side of the lens is intended to, ... i-n 



indicate the position of the canal of but adhering to the capsule all round a 



Petit. After Arnold. ,. , . . * M. A. 



little in front of its rim, after crossing the 



interval separating the tips of the ciliary processes of the choroid 

 from the lens. Thus the rim of the lens is not exactly at the 

 surface of the vitreous body, but buried slightly within it, and 

 overlapped a little by it. All round the rim of the lens, there is a 

 cavity in the vitreous body, extending under the circle of the ciliary 

 processes of the latter, and termed the canal of Petit (fig. 120, and fig. 

 116*). The hyaloid membrane constituting these ciliary processes 

 forms the anterior wall of this canal, which, by its adhesion to the 

 ciliary processes of the choroid, is subject to be drawn forwards by 

 the contraction of the ciliary muscle already described (p. 27). 

 When this occurs, the lens also is advanced, in consequence of the 

 union of this anterior wall of the hyaloid to its anterior surface near 

 the rim. Were the canal of Petit wanting, the ciliary muscle 



