of the Canal of PETIT. 235 



place. The eye was opened in about eight hours after the 

 death of the criminal : the foramen of SCEMMERING was remark- 

 ably distinct, and of a deep yellow tinge ; there was no fold, a 

 fact which proves this appearance to be a post mortem one, and 

 that SCEMMERING has on this point misled all anatomists since 

 his discovery. The retina was semitransparent. There were 

 several vessels on the surface of the retina, apparently veins 

 filled with dark blood ; none could be discovered traversing the 

 vitreous humour, for the reason, no doubt, that the branch which 

 is found to do so in the foetus of the mammalia, disappears in 

 very early life, and perhaps soon after the structure of the lens 

 is completed. 



The uses of this most mysterious part of the eye-ball, and 

 why it should exist only in certain classes of animals, and these, 

 too, differing widely from each other, are physiological problems 

 which seem to me of extremely difficult solution. 



Several pellucid vessels or fibres seem to connect the retina 

 and vitreous humor around, and near to, the entrance of the op- 

 tic nerve. They are spoken of by HALLER in the following 

 passage : " Vitrea membrana, simplex, intra retinam ex seipsa 

 oritur, nusquam observabili aliquo vinculo connexa, nisi Albinia- 

 nam arteriolam velis, aut vasa vitrea? membranee pellucida, quae 

 in ove et bove ad eamdem retinam parallela sublinit, non ob- 

 scura veniunt." 



The pulpy portion of the retina is not of uniform density, nor 

 is the membrane equally affected by the action of spirits : these 

 render the greater portion of it perfectly opaque, and of a slight 

 yellowish colour. But in the eye of the cat a large triangular 

 space, whose apex is at the entrance of the optic nerve, and base 

 externally and anteriorly, remains semitransparent, and compa- 

 ratively much thinner, than any other portion of the retina. 



With regard to the anterior termination of the retina, I may 

 remark, that I have not found any reason to alter the opinions 



