428 SPECIAL PHYSIOLOGY. 



vex, and supports the retina; in front, it is cup-shaped, for the recep- 

 tion of the crystalline lens. 



The crystalline lens, Fig. 83, Z, is a double convex, colorless, trans- 

 parent, firm body, placed in front of the vitreous humor ; it receives 

 its name from its crystal-like appearance and its lenticular shape. It 

 is inclosed in a transparent, structureless, highly elastic, and perme- 

 able membrane, called the capsule of the lens ; between the capsule 

 and the body of the lens is a single layer of transparent nucleated 

 cells ; these cells, after death, imbibe moisture, and then, breaking 

 down, form a liquid layer, the liquor Morgagni. The lens is chiefly 

 supported in its place by a transparent and highly elastic membranous 

 structure, called the suspensory ligament ; attached to the anterior 

 surface of the capsule, close to the margin of the lens, this ligament is 

 connected behind with the ciliary processes, and with the hyaloid 

 membrane, which incloses the vitreous body ; it may be traced as far 

 back as the ora serrata of the retina. It presents on its anterior sur- 

 face a number of folds, which fit in between the rays of the ciliary 

 processes. Around the margin of the lens, between the hyaloid mem- 

 brane and the suspensory ligament, is a circular passage, called the 

 canal of Petit. 



The posterior surface of the lens is embedded in the depression on 

 the forepart of the vitreous humor ; its anterior surface, which is free, 

 is placed in contact with the iris, behind the pupil. The superficial 

 portion of the lens is soft ; but towards the centre, it gradually be- 

 comes firmer and denser ; the central and firmest part is named the 

 nucleus. The posterior surface, Fig. 82, c?, is more convex than the 

 anterior; the curvature of both surfaces, the anterior of which is said 



Fig. 82. 



Fig. 82. Two diagrammatic views of the crystalline lens; a. anterior surface, showing the radiated ar- 

 rangement of its component bundles of fibres, which are here seen to meet on three plnnes; rf, side view, 

 or edge of the lens. The anterior flatter surface is here turned to the left hand, and the posterior more 

 convex surface, to the right. 



to be ellipsoidal and the posterior paraboloidal, incre 

 circumference ; its edges are rounded off. The lens 



araboloidal, increases towards the 

 measures about 



Jth of an inch in its antero-posterior diameter, and about Jd of an 

 inch transversely. The radius of the curve of its posterior surface is 

 about Jth of an inch ; that of the anterior surface varies, from some- 

 what more than Jth to about th of an inch. The substance of the 

 lens is composed of concentric layers, which are made up of micro- 

 scopic parallel fibres, by some said to be tubular (Kolliker) ; they 

 have uneven or indented margins, which fit together most accurately. 

 Towards the centre of the lens, these fibres meet in certain planes, , 

 which radiate from the central axis of the lens ; in the nucleus, there 

 are three principal planes ; in the superficial portion, there are as 



