VOL. LXXXVI.] PHILOSOPHICAL TKANSACTIONS, QQg 



the marsupium, extends to the capsula of the lens, and appears to be about half 

 the length of the marsupium itself. The union has been supposed to be ex- 

 tremely weak, because after death it readily gives way; this however is by no 

 means the case, for when it is coagulated in rectified spirits, it is not easily torn; 

 and the reason of its giving way in the dead eye, is probably from dissolution 

 readily taking place when surrounded by moisture. 



The anterior edge of the marsupium in some birds is narrower than its base, 

 as in the cassuary; in others, it is of the same extent, as in the turkey; and in all 

 I believe it is a uniform line; but when it is separated from the lens the folds 

 contract irregularly, and appear of different lengths. In the eagle the marsu- 

 pium is uncommonly strong. From the similarity of structure in the marsu- 

 pium and ciliary processes, as also their connection with the crystalline lens, I 

 was desirous of ascertaining whether the marsupium was possessed of any mus- 

 cular power, as this would determine the same point with respect to the ciliary 

 processes, and might lead to an explanation of the use of both these parts. 

 With this view I made the following experiments. 



The marsupium and crystalline lens of a goose's eye were exposed immediately 

 after death; and the lens was pushed forwards, by which means the marsupium 

 was elongated, and measured -^ of an inch; on taking ofF the pressure, it again 

 contracted to ^; this was repeated several times. The parts were then left, 

 till it was supposed that all remains of life were gone, and the same experiment 

 was repeated. In the stretched state it measured as before, ^ of an inch, but 

 in the contracted state, 4 ; this change arose from the elasticity of the ligament 

 connecting the marsupium to the bottom of the eye; and therefore the contrac- 

 tion of -J-s; which was now lost, must have arisen from some other cause. The 

 result of this experiment favours the idea, that the marsupium possesses a mus- 

 cular power, but in matters where we are so liable to be deceived, it seemed not 

 a sufficient proof; I therefore made several other experiments, but they were all 

 liable to some objections; the following however appears satisfactory, and shows 

 that there is a power of contraction in the marsupium independent of elasticity. 



The crystalline lens of a turkey's eye was extracted, and immediately after- 

 wards the turkey was killed, by wounding the spinal marrow; the 2 eyes were 

 taken out, and put into spirits.* In the one, the marsupium h.ad nothing to 

 prevent its contracting to the utmost; while in the other, the lens being in its 

 natural situation, could not allow of any unusual contraction. Some days after, 

 the 1 eyes were examined; in the perfect eye the marsupium measured -5I5- of an 

 inch, and the different folds of it were .semi-transparent; in the imperfect eye 



* In the act of dying, the muscles are found to contract to their utmost, where there is no re- 

 sistance to prevent such action ; this is also found to take place in the greatest degree, when the 

 animal U killed by any violence committed on the brain, or spinal marrow. — Orig. 



