STRUCTURE OF THE CRYSTALLINE LENS. 



265 



Fig. 58. 



lens; a, cells connecting the 

 >, fibres of the lens, 



Structure of the 



body of the lens fo 



with slightly sinuous edges (human); c, ditto from the Ox,with 

 finely serrated edges; d, ditto from the Cod; the teeth much 



condition of this structure, incised wounds commonly heal very readily, as is 

 well seen after the operation of extraction of Cataract ; but the foregoing details 

 make evident the importance of not carrying the incision further round than is 

 necessary ; since the corneal tissue should not be cut off from the supply of 

 nourishment affdrded by the vessels in its immediate proximity. 



255. The Crystalline Lens of the Eye approaches cartilage, in its structure 

 and mode of nutrition, more nearly than towards any other tissue. It may be 

 separated into numerous laminae, which are composed of serrated fibres that lock 

 into one another by their delicately-toothed margins 1 (Fig. 58, b, c, d)', these 

 serrations, however, are much 

 less obvious on the margins of 

 the fibres of the human crystal- 

 line, than they are in those of 

 the lenses of fishes. Each fibre 

 appears to be made up of a series 

 of cells, which coalesce with each 

 other at an early period; and 

 these are indicated, even in the 

 fully-formed fibres, by nuclei 

 which present themselves at 

 pretty regular intervals in their 

 substance. A layer of uncon- 

 verted cells (a), extremely thin 

 and transparent, of unequal size, 

 and nucleated, is always found 

 between the surface of the lens 



and its capsule, which it brings coarser. Magnified 320 diameters. 



into organic union. The capsule 



is perfectly transparent, homogeneous, and very elastic ; it forms a perfectly close 

 envelop, admitting neither vessels nor nerves to the contained lens ; but it is 

 very readily permeable to fluids, as is shown by the absorption from the aque- 

 ous humor that sometimes takes place after death, giving rise to the so-called 

 " liquor Morgagni," the presence of which, according to Mr. Bowman (Op. cit., 

 p. 70), is not the normal condition. The lens itself is at no period of its exist- 

 ence supplied with bloodvessels, these being confined to the capsule. During 

 the early part of foetal life, and in inflammatory conditions subsequently, both 

 the anterior and posterior portions of the capsule are distinctly vascular; the 

 latter being supplied from the arteria centralis retinae, which expands upon it 

 after having traversed the vitreous humor, and sends branches that pass round 

 the margin, to be distributed, with twigs from the ciliary processes, upon the 

 anterior surface. The loops formed by the latter gradually retreat, during foetal 

 life, from the centre towards the margin, like those of the synovial membranes ; 

 and after a time the posterior capsule also ceases to be vascular. The subsequent 

 growth of the crystalline lens appears to be very trifling, and appears to be suffi- 

 ciently provided for by imbibition through its capsule, from the aqueous and 

 vitreous humors which are in contact with its two surfaces respectively. The 

 substance of which the lens is composed seems to be chemically identical with 

 the Globulin of the blood-corpuscles ( 23); it contains about 58 per cent, of 

 water. Cases of the regeneration of the crystalline lens, after its complete re- 

 moval by extraction, have been put upon record ; but such a reparation must be 

 extremely rare, and is probably limited to young subjects. The Vitreous body 

 has been commonly supposed to consist of a loose fibrous network, the areolse of 

 which are filled up with fluid, that drains away slowly when the membrane is 



See Sir David Brewster, in "Philos. Transact.," 1833. 



