HISTOLOGY OF THE VITREOUS HUMOUR. 355 



the foundation of the incorrect statement that the fibres of the 

 zonula are the direct prolongation of the limitans. If, however, 

 the vitreous with the zonula and lens be macerated for several 

 weeks in a ten per cent, solution of common salt, the connec- 

 tion 'between the zonula fibres and the limitans is loosened, and 

 the isolation of the two structures is rendered easier. 



The fibres of the zonula, as they extend forward towards the 

 ciliary processes, coalesce in part to form fibres which pro- 

 gressively increase in thickness, so that the free portion of the 

 suspensory ligament of the lens (which aids in forming the 

 posterior wall of the posterior chamber of the eye) contains the 

 thickest fibres ; in great part, however, they also run nearly 

 unchanged in diameter from the ora serrata to the sequator 

 lentis. It has already been stated that at this latter point 

 they again break up into extremely fine fasciculi. 



In a meridianal section of the eye the zonula presents the 

 appearance of resting with a triangular base upon the sequator 

 lentis. This triangular area is completely occupied by the 

 terminal fibrils of the zonula fibres, but at the same time con- 

 tains no cavities, and has not been mistaken by any one except 

 Merkel for the canal of Petit. 



The fibres of the zonula are neither connective-tissue nor 

 elastic fibres. Their relations, both chemical (as with acids and 

 alkalies) and physical, show that they are different from either. 

 It would be rash, however, as has recently been done, to regard 

 them as being muscular. Comparative anatomical and em- 

 bryological researches, which can alone be appealed to in order 

 to settle the real nature of these fibres, are at present wanting. 



The zonule of Zinn forms the anterior wall of the canal of 

 Petit. The posterior wall is formed by the smooth surface of 

 the vitreous. The tissue of the vitreous is condensed at this 

 part, just as the membrane of Bowman is a condensation of 

 the tissue of the substantia propria of the cornea. There is 

 here no independent membrane or hyaloid ea. The canal of 

 Petit commences at a distance of from four to five millimeters 

 from the ora serrata, and reaches not only to the sequator of 

 the lens, but for two millimeters on the posterior capsule of 

 the lens towards the posterior pole of that body. 



It is difficult to determine whether there is really a space 



AA 2 



