140 On the Fossa Patellarin of tl,, 



\'iin'mn. [F<-!.. .". 



of the vitreous substance, but the membrane is no such thing; it is 

 a true membrane; it can readily be isolated, stained, submitted to 

 microscopical examination, Ac. 



Even with the unstained vitreous, it is quite easy to introduce a 

 blunt instrument through a puncture in the membrane and, by working 

 the instrument about under the surface, to detach the membrane 

 from the surface of the vitreous substance. 



When this has been done, a bell of air blown under it displays the 

 membrane to good advantage as a delicate, elastic, smooth, apparently 

 structureless, perfectly transparent sheet of tissue, answering most 

 completely to the terra " hyaloid." Though delicate, it is yet strong 

 enough to support the whole weight of the vitreous when a blunt in- 

 strument is put into it. 



When, the bounding membrane remaining intact, the vitreous is 

 squeezed so as to bulge its anterior face, that face does not bulge 

 equally all over its extent. The centre of the anterior face projects 

 more than the peripheral ring. The central projected part corre- 

 sponds to the fossa patellaris, where, as I shall show, the patellar mem- 

 brane is thin, while the peripheral ring forms the back wall of the 

 canal of Petit, and here the membrane is comparatively thick. The 

 transition from the peripheral to the central parts is fairly sudden, 

 for the central elevation rises from a distinct line corresponding to the 

 inner margin of the peripheral ring. The canal of Petit is, therefore, 

 a true canal. 



If the vitreous be inverted over the mouth of a test-tube (with a hole 

 in the bottom of it) of about inch diameter, and tied over it with a 

 thick silk thread, and afterwards with a rubber band, the superficial 

 part of the hyaloid and greater mass of the vitreous is cut through. 

 If now the vitreous substance be carefully pulled off by forceps, or if 

 the test-tube be set upright in a beaker, and water poured into the 

 beaker, the water rising in the tube will bulge the membrane so that 

 the vitreous substance will drain off it in an hour or so. The 

 membrane thus isolated is toughened by exposure over night, so that 

 such a membrane, though it looks like a mere film, yet sustained no 

 less a pressure than 40 inches of water ; others sustained 22, 28, 

 34 inches, and so on, even after having been dead for days. 



If the membrane be snipped all round its periphery, it can be 

 detached as a whole from the subjacent vitreous substance. 



When it has been removed, little tags of deeply-staining material 

 are sometimes seen projecting from its deep face ; these, I have 

 thought might be vestiges of the hyaloid artery ; but, whether these 

 are there or not, there is little or no adhesion between the membrane 

 and the vitreous substance. 



When removed, and its deep surface brushed under water 

 remove any adherent vitreous substance, it is seen to be a hyaloic 



