8o 
Dr. Young’s Lecture 
Haller had very truly asserted, merely duplicatures of a 
membrane, which, when its ends are cut off, may easily be 
unfolded under the microscope, with the assistance of a fine hair 
pencil, so as to leave no longer any suspicion of a muscular 
texture. The experiment related by Mr. Home,* can scarcely 
be deemed a very strong argument for attributing to this sub- 
stance a faculty which its appearance so little authorises us to 
expect in it. The red substance in the choroid of fishes, 
(Plate VII. Fig. 55.) is more capable of deceiving the observer; 
its colour gives it some little pretension, and I began to examine 
it with a prepossession in favour of its muscular nature. But, 
when we recollect the general colour of the muscles of fishes, 
the consideration of its redness will no longer have any 
weight. Stripped of the membrane which loosely covers its 
internal surface, (Fig. 56.) it seems to have transverse divi- 
sions, somewhat resembling those of muscles, and to termi- 
nate in a manner somewhat similar; (Fig. 57.) but, when 
viewed in a microscope, the transverse divisions appear to be 
cracks, and the whole mass is evidently of a uniform texture, 
without the least fibrous appearance ; and, if a particle of any 
kind of muscle is compared with it, the contrast becomes very 
striking. Besides, it is fixed down, throughout its extent, to 
the posterior lamina of the choroid, and has no attachment 
capable of directing its effect ; to say nothing of the difficulty 
of conceiving what that effect could be. Its use must remain, 
in common with that of many other parts of the animal frame, 
entirely concealed from our curiosity. 
The bony scales of the eyes of birds, which were long ago 
described in the Philosophical Transactions by Mr. Ranby, 
• Phil. Trans, for 1796. p. 18. 
$ Phil./Trans. Vol. XXXIII. p. 223. Abr. Vol. VII. p. 435. 
