Canal of Petit^ and the Marsupium Nigrum. S25 
Observations on the Comparative Anatomy of the Eye,” more 
careful dissections have not confirmed. It was supposed, for ex- 
ample, that this membrane might be one of the sources of the 
pigmentum nigrum, but in the most minute vascular injec- 
tions, prepared with the greatest care, no vessels can be tra- 
ced to the membrane of Jacob. It is not wanting over the 
tapetum, as was imagined, but merely becomes transparent, 
thus altering very singularly its colour, according to the struc- 
ture and colour of those portions of the choroid with which it 
is contiguous. Several facts seem to shew, that the membrane 
of Jacob is altogether inorganic, and analogous to the coloured 
portion of the rete mucosum of the skin. 
3 . Of the Annulus albus. 
This body proves to be vascular, and to have a structure 
somewhat analogous to the iris. 
I am. My dear Sir, with great esteem, yours sincerely, 
To Dr Buewster, 7 
Sec. R. S. E. ^c. ^c. 3 
R. Knox, 
Art. XXI. — A short Accomit of some Observations made in 
France^ to investigate the Parallaxes of the Fixed Stars. 
Two Reports were made, a considerable time ago, one to the 
French Institute, and the other to the French Board of Longi- 
tude, respecting the observations of M. Le Comte D’Assas de 
Montdardier, Capitaine de Vaisseau, Chevalier de St Louis, &c. 
&c. for determining the parallax of the fixed stars. These ob- 
servations have scarcely been heard of in this country ; and we 
extract a short account from the Report to the Board of Longi- 
tude, made by M. Delambre, a short time before his death ; he, 
M. de Rossel, and M. Biot, having been appointed a committee 
for that purpose. The report from the Board of Longitude is 
much fuller than that to the Institute. Both are very favour- 
able ; and it appears, that, in consequence of the report of the 
