23 



name. ' * Hyaloid portion of the' vitreous body ' ' might be more de- 

 scriptive of its real structure. Szent-Gyorgyi suggests tractus hya- 

 loideus corporis vitrei. Its essential structure is given at this stage 

 of development; only minor modifications are observed in the eye 

 of the adult animal. 



The description of the formation of the hyaloid canal leads us 

 also to a better appreciation of the structure of the vitreous body 

 as a whole. The complex structure of the preceding period, owing 

 to the invasion by great masses of mesoderm, has disappeared 

 through a process of disintegration and resorption, and has given 

 place to a much simpler and more regular arrangement of the fibers. 

 The rather strong fibers of the pars ciliaris, already observed in 

 embryos of 60 and 80 mm length, have in the meantime assumed 

 the appearance of fiber bundles (Figure 19), the arrangement of 

 which has already been described at length. There is no longer 

 evidence of an extensive union between these fibers, each bundle be- 

 ing more or less independent of the others. But their place of 

 origin is the same, the cells of that portion of the ciliary retina, 

 immediately anterior to the ora serrata. The ectodermal origin 

 and nature of the permanent vitreous body is, therefore, no less 

 certain than that of the primitive vitreous body. The mesoderm 

 has no share in its production. 



The vitreous body in the eye of the adult animal differs only 

 in minor details from that described so far. Comparing figures 17 

 and 19, we notice that the hyaloid artery has entirely disappeared. 

 The fibers of the vitreous body and the zonula ciliaris have essen- 

 tially the same arrangement and structure (Figures 15 and 16). 

 The shape of the hyaloid canal, however, has slightly changed. By 

 a further ingrowth of the vitreous fibers in the region of the lens, 

 the funnel-like shape of the preceding stages (Figures 17 and 18) 

 has given place to a structure of almost uniform diameter through- 

 out its entire length (Figures 19 and 22). This tissue, however, 

 shows no tendency to condensation or growth which might lead to 

 a gradual obliteration of the canal. The latter was found in the 

 eyes of every specimen examined, forty in all. Wolf rum's state- 

 ment, therefore, that the hyaloid canal is not a constant structure 

 of the eye of the adult pig, but is found only occasionally and then 

 always in connection with remnants of the hyaloid artery, is not 

 in accordance with the facts. Only in two eyes, out of a total of 



