1476 HUMAN ANATOMY. 



the lens equator. The fibres are so closely interlaced that it is possible to inject aii 

 between them and so produce a beaded ring surrounding the lens. This appearance 

 was long interpreted as demonstrating the presence of a delicate channel, the ca7ial 

 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. 



In addition to the chief zonular fibres, accessory bands occur, some of which 

 pass from the ciliary processes to the long zonular fibres, whilst others extend from 

 point to point on the ciliary processes. 



The origin of the vitreous body and of the suspensory ligament has long been and still is a 

 matter of dispute. The fact that these structures are very closely connected, that fibres from the 

 suspensory ligament pass through the vitreous, and, in some cases at least, end in that body, 

 renders it probable that the two structures have a common genesis. Anatomists are divided, 

 however, in their views, some believing the structures in question to be derived from the 

 mesoblast which enters the choroidal cleft with the blood-vessels, whilst others assign to them 

 an ectoblastic origin, the primary vitreous tissue being from the retina (inner wall of the second- 

 ary optic vesicle). In many of the lower animals the vitreous contains no blood-vessels, and, 

 further, since the vitreous is formed without the presence of embryonal connective tissue, 

 the presumption is strong that the vitreous arises from the retina. That the ectoblast in mam- 

 mals, however, is the sole source of the vitreous has not been proven ; moreover, the close 

 histological resemblance of the vitreous to embryonal connective tissue suggests with much force 

 the probability that the mesoblast has a considerable share in the formation of the vitreous body. 



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 percentage of albumin. It is 

 produced chiefly by the blood-vessels of the ciliary processes, the iris taking probably 

 little or no part in the process. The albumin of the blood is separated by the action 

 of the double layer of cells covering the pars ciliaris retinae, which act either as a filter- 

 ing medium (Leber), or as a secreting epithelium (Treacher Collins). The aque- 

 ous humor is constantly being produced and is carried off through the spaces of 

 Fontana into the canal of Schlemm, and also through the lymph-spaces in the iris, 

 its quantity being an important factor in determining intraocular tension. With the 

 exception of a few migratory leucocytes, the aqueous humor is devoid of morpho- 

 logical elements. 



The space occupied by the aqueous humor is incompletely subdivided by the 

 iris into two compartments, the anterior and posterior chambers. The anterior 

 chamber (camera oculi anterior) is bounded in front by the cornea, and behind by 

 the iris and lens, and has a depth at its centre of from 7.5-8,5 mm. The posterior 

 chamber (camera oculi posterior) is the small annular space, triangular in cross-sec- 

 tion, which has for its anterior boundary the iris, and 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 poste- 

 rior chamber, are filled with aqueous humor, and are, therefore, only a part of the 

 posterior chamber. 



Practical Considerations. — When the cornea is perforated as by a wound 

 or by ulceration, the aqueous is forced through the opening so rapidly that the iris 

 is swept along by it, and unless great care is observed it will become adherent to the 

 margin of the corneal opening (anterior synechia). 



The aqueous humor is of importance in the removal of foreign matter. Blood 

 will often be removed in a few days. Suppuration of the adjacent tissue may lead 

 to the collection of pus in the anterior chamber (hypopion). Hyphsemia is a collec- 

 tion of blood in this chamber, and of itself is not a grave condition, although it may 

 be a sign of a more serious disease. 



