442 CRYSTALLINE LENS. 



Fig. 197.* The posterior surface of this tunic 



adheres firmly to the tunica hyaloidea, 

 with which it is in contact : and this 

 last .membrane is generally ruptured in 

 the attempt to separate them, although the separation can 

 sometimes be effected without rupture. 



The anterior surface is so intimately connected with that 

 lamen of the hyaloid tunic which passes before it from the 

 canal of Petit, that it is not separable without laceration ; and 

 it, therefore, has not been ascertained, whether or not this 

 lamen extends completely over the surface. 



As the capsule of the lens is thus connected with the tunica 

 hyaloidea, and this last mentioned tunic adheres to the ciliary 

 body, it necessarily follows that the lens is confined in its 

 proper position behind the pupil. 



Notwithstanding the soft consistence of the exterior portion 

 of the lens, there is reason to believe that it has a peculiar 

 organization ; for if it be immersed some time in a diluted solu- 

 tion of the nitrate or muriate of alumina, or in several other 

 fluids, and then dried, it will be found to be composed of con- 

 centric lamellae, which resemble those of the bulbous roots ; 

 and these lamellae will appear to consist of fibres. 



It has been supposed that muscular fibres entered into the 

 composition of the crystalline lens, but this opinion has never 

 been generally adopted. f 



Between the lens and capsule a small quantity of a trans- 

 parent fluid is sometimes found, which escapes whenever the 

 capsule is punctured. This fluid is supposed to be most abun- 

 dant on the anterior surface, and is called liquor Morgagni. 

 The lens, according to Berzelius, consists of a peculiar 



* Fig. 197 shows the difference of convexity in the lens at different periods 

 of life, as represented by Soemmering. To the left is the lens of a fcetus. The 

 middle one is that of a child six years of age ; the right is that of Sin adult. The 

 lens varies in consistence as well as color, as life advances. In infancy it is 

 soft and pulpy, in youth firmer, so as readily to be crushed between the thumb 

 and finger and in old age it becomes tough and firm. Hence the operation 

 of cutting up the lens for the cure of cataract, is more appropriate in children 

 than old persons, in whom, from its toughness, it is apt to roll under the needle 

 and inflict injury on the iris. p. 



f See Dr. Young's Memoirs in the Philosophical Transactions for 1793. 



