THE VITREOUS BODY. 



355 



FIG. 406. Portion of lens and 

 its capsule; A, section through 

 equator; a, capsule ; 6, epithelial 

 cells, which at z transform into 

 lens-fibres (/) with nuclei (); B, 

 fragment of capsule (A) with epi- 

 thelium (e), surface view. X 130. 



artery are temporary structures and usually disappear before birth. Excep- 

 tionally they may persist, the tunic being represented by the pupillary mem- 

 brane and the artery by a fibrous strand within the 

 vitreous, stretching from the optic disk towards 

 the lens. 



The anterior portion of the capsule is lined by 

 a single layer of flat polygonal cells, the epithelium 

 of the lens capsule, which represents morphologi- 

 cally the anterior wall of the original lens-vesicle. 

 On approaching the equator of the lens, these cells 

 become elongated and gradually converted into 

 the young lens-fibres, whose nuclei lie in the super- 

 ficial part of the lens. 



The lens-substance is composed of long 

 flattened fibres, in cross- sections of compressed 

 hexagonal outline, 5-1 1 /-* broad and 2-4 p thick, 

 held together by an interfibrillar cement-substance. 

 These fibres are modified epithelial elements, 

 which develop by the elongation of the original 

 ectodermic cells of the posterior layer of the primary 

 lens-vesicle. The subsequent growth of the lens 

 depends upon a similar modification of the anterior 

 capsule-cells, the region where this transformation occurs being known as 

 the transitional zone. The individual lens-fibres vary greatly in length, 

 those forming the outer layers being longer and thicker than those which 

 constitute the centre of the lens. The edges of the fibres are finely 

 serrated, and, as the points of the serrations of adjacent fibres are in contact, 

 fine intercellular ghannels are left for the passage of nutritive fluid. 



THE VITREOUS BODY. 



The vitreous body fills the space between the lens and the retina, being 

 in close contact with the retina and acting as a support to it as far forwards 



as the ora serrata. Here it 

 separates from the retina and 

 passes to the posterior surface 

 of the lens, presenting a shallow 

 depression, the hyaloid or pa- 

 tellar fossa, on its anterior 

 surface for the reception of the 

 lens. The fresh vitreous is 

 semifluid, perfectly transparent 

 and consists of about 98.5 per 

 cent, of water. 



The vitreous possesses 

 a framework of delicate un- 

 branched fibrils, which pass in 

 all directions through the vitre- 

 ous space and form the meshes 

 in which the fluid constituents 

 of the mass are held. The 



I 



vitreous body, showing feltwork of 

 bres and remains of cells X 450. (Ketzius.) 



mass are 

 surface of the vitreous is en- 



closed by a delicate boundary layer, called the hyaloid membrane, 

 formed by condensations of the fibrils, arranged parallel to the surface and 



