VOL. LXXXV,] PHILOSOPHICAL TRANSACTIONS. 45^ 



■^ part of an inch ; and on removing it, the cornea recovered itself to its ori- 

 ginal length. In different trials it varied in the quantity of elongation^ but in 

 all of them it was fully Vt part of the whole length, or diameter of the cornea. 



The elasticity of the cornea being thus ascertained, encouraged me to proceed 

 in the anatomical investigation ; and I was desirous of determining more exactly 

 than had hitherto been done, the precise insertion of the tendons of the 4 

 straight muscles of the eye, so as to know whether their action could be ex- 

 tended to the cornea or not. In dissecting these muscles to their termina- 

 tion, I found that they approached within -f of an inch of the cornea, before 

 their tendons became attached to the sclerotic coat on which they lay ; it was 

 evident that they did not terminate at this part, but were so united as to be diffi- 

 cultly separated by dissection ; I therefore endeavoured by gentle force to puU 

 them asunder, as in that way the parts would separate in the direction of their 

 fibres. In doing this, they not only admitted of separation to the edge of the 

 cornea, but brought away a lamina of the cornea with them. I thought this 

 would be better seen in an eye after putrefaction had begun to take place, but 

 found that in that state it could scarcely be demonstrated ; while in the recent 

 eye the whole of the external lamina of the cornea could be brought away along 

 with the 4 straight muscles, leaving the surface underneath uniform, but without 

 polish, and on the same plane with the sclerotic coat, of which it was a conti- 

 nuation. As this was a new fact, and a very important one, showing a connec- 

 tion between these muscles and the cornea, I have dried the parts, and preserved 

 them in that state, to show the mode in which the tendons of the straight 

 muscles are lost in the cornea, giving it the appearance of a central tendon. 

 The cornea from this investigation is proved to be composed of two laminas, the 

 external a continuation of the tendons of the 4 straight muscles, the other a 

 continuation of the sclerotic coat, and the uniting medium between them is not 

 unlike very fine cellular membrane. 



When the cornea is examined at its attachment to the sclerotic coat and ten- 

 dons of the straight muscles, it appears to be of exactly the same thickness with 

 those parts, but grows thicker towards the centre ; this increase of thickness is 

 principally in the external lamina ; for when that is removed, the other appears 

 equally so through its whole extent. To ascertain that the cornea is really 

 thickest in the middle, I made a transverse section of it, and Mr. Ramsden, with 

 several other gentlemen, examined the cut edge through a magnifying glass, and 

 all of them were satisfied with the fact of the central part being evidently thicker 

 than that which was nearer to the circumference. In stretching the cor- 

 nea, the central part yields most readily to the power applied ; this is so much 

 the case, that if the cut edge of the cornea be examined while it is several times 



3 N 2 



