THE "AQUEOUS CHAMBER. 357 



circumlental space to find attachment into the capsule of the lens. 

 Some of the fibres are inserted anterior to the equator, others posterior to 

 the equator, and some directly into the margin. Those inserted ante- 

 riorly arise behind and chiefly from the valleys between the ciliary processes, 

 whilst those inserted into the equator come from the elevations of the proc- 

 esses. As they diverge to gain their insertion in the lens-capsule, the cross- 

 ; ng fibres enclose an annular space, triangular in section, whose base is di- 

 rected towards the lens equator. The fibres are so closely interlaced that it 

 is possible to inject air between them and so produce a beaded ring surround- 

 ing the lens. This appearance was long interpreted as demonstrating the 

 presence of a delicate channel, the canal of Petit, encircling the lens. The 

 existence of a definite channel, however, is no longer accepted, the space 

 capable of inflation being part of the larger circumlental space, which is 

 filled with fluid and communicates, by means of fine clefts, with the posterior 

 chamber. 



THE AQUEOUS HUMOR AND ITS CHAMBER. 



The aqueous humor is the transparent fluid which fills the space between 

 the anterior surface of the vitreous body and the posterior surface of the 

 cornea. In chemical composition it closely resembles water, containing only 

 traces of albumin and extractives, and differing from lymph in its low per- 

 centage of albumin. It is derived chiefly from the blood-vessels of the cili- 

 ary processes by the action of the double layer of cells covering the pars 

 ciliaris retinae. The aqueous humor, constantly produced, is carried off 

 through the spaces of Fontana into the canal of Schlemm, and also through 

 the lymph-spaces in the iris. With the exception of a few migratory leuco- 

 cytes, the aqueous humor is devoid of morphological elements. 



The space occupied by the aqueous humor is incompletely subdivided 

 by the iris into two compartments, the anterior and posterior chambers of 

 the eye. The anterior chamber is bounded in front by the cornea and 

 behind by the iris and lens, and has a depth at its centre of from 7.58.5 

 mm. The posterior chamber is the small annular space, triangular in 

 cross-section, which has for its anterior boundary the iris, is limited laterally 

 by the ciliary processes, and medially and posteriorly by the lens and the 

 vitreous body. The spaces between the fibres of the suspensory ligament 

 communicate with the posterior chamber, are filled with aqueous humor, 

 and are, therefore, only a part of the posterior chamber. 



THE EYELIDS AND CONJUNCTIVA. 



The eyelids or palpebra are two movable folds of integument an 

 upper and a lower strengthened along their free margins by a lamina of 

 dense fibrous tissue, the tarsal plate, and modified on their deeper aspect so 

 that this surface resembles a mucous membrane, the conjunctiva. The free 

 border of the lid presents a well-defined posterior margin, along which open 

 the minute ducts of the tarsal glands, whilst the anterior margin is rounded 

 and passes insensibly into the adjoining external skin-surface and is beset 

 with the eyelashes. The latter, the cilia, are stiff outwardly curving hairs, 

 which number from 150-175 in the upper lid and about half as many in the 

 lower. That part of the narrow conjunctival sac which covers the posterior 

 surface of the lids constitutes the patyebral conjunctiva and that reflected 

 onto the eyeball is the bulbar conjunctiva, while the bottom of the groove, 

 where these two portions are continuous, is known as the form'* conjunctivas. 

 The lachrymal lake is the shallow bay into which the conjunctival sac is pro- 



