DEVELOPMENT OF THE EYE. 



737 



AQUEOUS HUMOUR AND ITS CHAMBER. 



The aqueous humour fills the space in the fore part of the eyeball, be- 

 tween the cornea and the capsule of the lens with its suspensory ligament. 

 The iris, resting in part upon the lens, divides the aqueous chamber partially 

 into two. The aqueous humour differs little from water in its physical cha- 

 racters ; but it contains a small quantity of some solid matter, chiefly chlo- 

 ride of sodium, dissolved in it. 



The chambers, into which the space containing the aqueous humour is di- 

 vided by the iris, are named respectively the anterior and posterior. This 

 subdivision is incomplete in the adult, but in the foetus before the seventh 

 month it is completed by means of the inembrana pupillaris, which by its 

 union with the margin of the pupil closes the aperture of communication be- 

 tween the two chambers. 



The anterior chamber is limited in front by the cornea and behind by the 

 iris, while opposite the pupil it is bounded by the capsule of the lens. 



The posterior chamber was originally so named in the belief that a free 

 space intervened between the iris and the capsule of the lens. It is now, 

 however, well ascertained by observations on the living eye, and by sections 

 made in the frozen state, that the pupillary margin and part of the posterior 

 surface of the iris are in contact with the capsule of the lens ; and the term 

 posterior chamber can therefore be employed only to indicate the want of 

 continuity between those opposed structures, where no space actually inter- 

 venes, and to the angular interval existing at the circumference between the 

 ciliary processes, the iris, and the suspensory ligament. 



DEVELOPMENT OF THE EYE. 



The eyes begin to be developed at a very early period, in the form of two hollow 

 processes projecting one from each side of the first primary cerebral vesicle. Each 

 process becomes converted into a flask-shaped vesicle, called the primary optic vesicle, 

 which communicates by a hollow pedicle with the base of the posterior division of the 

 first primary cerebral vesicle. (See p. 578, and fig. 386 B.) According to the obser- 

 vations of Remak on the chick, the pedicles, originally separate, come together, and 

 their cavities temporarily communicate, a condition which may explain the forma- 

 tion of the optic commissure. The primary optic vesicle comes into contact at its 

 extremity with the cuticle, which somewhat later becomes invaginated at this point, 

 and forms a small pouch pressing inwards on the optic vesicle ; the aperture of this 



Fig. 490. LONGITUDINAL SECTION 

 OP THE PRIMARY OPTIC VESICLE 

 IN THE CHICK MAGNIFIED (from 

 Remak). 



A, from an embryo of sixty-five 

 hours ; B, a few hours later ; C, 

 of the fourth day ; c, the corneous 

 layer or epidermis, presenting in 

 A, the open depression for the 

 lens, which is closed in B and C ; 

 I, the lens-follicle and lens; pr, 

 the primary optic vesicle ; in A 

 and B, the pedicle is shown ; in C, 



the section being to the side of the palicle, the latter is not shown; v, 

 ocular vesicle and vitreous humour. 



the secondary 



pouch becomes constricted and closed, and the pouch is soon converted into a shut 

 sac, within which the contents subsequently becoming solid form the lens and its 

 capsule. After the lens has been separated from the cuticle, the deeper tissue sends a 



o C 



