THE BALL OF THE EYE. 429 



however, varies its shape in a remarkable degree at the differ- 

 ent periods of life; immediately after birth it is spheroidal, in 

 about six years afterwards its lenticular shape is well marked, 

 and, subsequently, it becomes more flat and thin. 



The lens naturally is perfectly transparent. In the greater 

 part of its thickness it has the consistence of half dissolved glue, 

 but its centre is much more solid; this change, however, is ef- 

 fected successively. When it is subjected to the mineral acids, 

 to heat, to alcohol, and several other agents, it becomes much 

 more solid throughout; it may then be separated, like an onion, 

 into a series of concentric lamellae, subdivisible into longitudi- 

 nal fibres. Besides these, there are fibres more or less oblique 

 which hold the Iarrella3 together. These arrangements prevail 

 from the centre to the circumference of the lens; and between 

 the lamina? there is a diaphanous humour resembling that be- 

 tween it and its capsule.* 



The lens is invested by a capsule which is a complete sac, 

 having exactly its shape, but separated from it, to a very in- 

 considerable extent, by the transparent humour just alluded to, 

 called the Liquor Morgagni. The capsule is covered in front 

 by a layer of the tunica hyaloidea adhering very closely to it, 

 but which, in one instance, I was enabled to peel off partially 

 in the eye of a sheep, from one side to the other. The capsule 

 is covered, in like manner, on its posterior face by the tunica 

 hyaloidea; but the two may be separated there more easily, 

 according to the observations of Bichat. S<me of the most 

 distinguished continental anatomists are decidedly in favour of 

 the capsule of the crystalline being a complete bag; but it is 

 rather unsettled whether the exterior margin of the capsule 

 bounds the lesser circumference of the canal of Petit, or whe- 

 ther the two layers of the tunica hyaloidea unite previously at 

 the circumference of the capsule. The latter seems to be the 

 opinion of M. J. Cloquet. The late Dr. Physick, in some cases 

 of membranous cataract, has succeeded in drawing out the 

 capsule entire, so as to exhibit its whole extent when floated 

 in water. 



The capsule in front of the lens is much thicker than the tu- 

 nica hyaloidea, and its difference of character from the latter 



* J. F. Meckel. 



