228 JOHN DENIS MACDONALD. 
part alone a distinct epithelial coat is said to be found. 
According to this, the posterior elastic lamina is the true 
basement of the restricted membrane of the aqueous 
humour, and the disease previously known as aquo-capsulitis 
must receive anew signification. The foregoing facts and 
considerations, however, seem to me to be rather in favour 
of the former doctrine, added to which it is further known 
that the iris also is covered with a fine epithelium. ‘Thus, 
besides the three coats and three humours, three struc- 
tureless capsules appertaining to the latter may be recog- 
nised in the eye as of old. But to return from this apparent 
digression to the more immediate subject of the paper, I 
must state that much difference of opinion still exists amongst 
histologists as to the real nature of the fibrous tissue which 
is said to originate in a transformation of the border of 
Descemet’s membrane in its entire thickness. I am led to 
think, however, that the conflicting views on this subject 
will be reconciled when it is known that the tissue alluded 
to carries with it, as it were, a glaze or delicate coating of 
the homogeneous hyaline material of which the elastic lamina 
itself is composed (this is of course quite distinct from the 
epithelium which, unless detached during the process of 
examination, is found coating the structure). Indeed, this 
must have been observed by Mr. Bowman, who, from the 
appearances presented to him, drew the very rational and 
natural deductions embodied in the quotation from Kolhker 
above made. 
The attachment of the posterior elastic lamina to the 
cornea proper can scarcely be said to be very intimate. On 
the contrary, it is quite easily detached, if not as a whole, at 
least in shreds. Its tendency to roll up in the direction of 
its convexity is doubtless one of the means by which its con- 
tact with the cornea is preserved. But if, in accordance 
with existing views, the whole or a considerable part of the 
contractility of the iris and ciliary muscles were to be 
brought directly to bear upon the border of the elastic 
lamina, it 1s easy to conceive that a hitherto unthought-of 
class of lesions would be frequently witnessed by ophthalmic 
surgeons. By the beautiful mechanism pointed out in this 
paper, however, nature has provided against the possible 
occurrence of such lesions, and thus, while the border of 
Descemet’s membrane is pinned down, so to speak, to the 
fibrous cornea, forcible traction is communicated to this 
latter structure chiefly, and not to the elastic membrane 
alone. If there is no fallacy in this reasoning, or in the 
interpretation of the facts upon which it is founded, a more 
