1474 HUMAN ANATOMY. 



composed of delicate, apparently unbranched fibrils, which pass in all directions 

 through the vitreous space and form the meshes in which the fluid constituents of 

 the mass are held. The surface of the vitreous is enclosed by a delicate boundary 

 layer, called the hyaloid membrane, formed by condensations of the fibrils, 

 which are here arranged parallel to the surface, and closely felted. It is, however, 



not a true membrane, but only a con- 

 densation of the vitreous fibres. The 

 vitreous is attached firmly to the retina 

 at the nerve entrance and at the ora 

 serrata, between these points the hya- 

 loid being indistinct. As the vitreous 

 leaves the retina, the boundary layer 

 becomes thicker, in some cases to be- 

 come thin again or absent in the region 

 of the patellar fossa. 



The central part of the vitreous is 

 occupied by a channel, the hyaloid 

 canal, also known as the canal of Slil- 

 ling or the canal of Cloqiict, which is 

 about one millimeter w r ide and extends 

 from the optic entrance toward the pos- 

 terior pole of the lens. During foetal 

 life this canal lodges the arteria hya- 

 Portion of adult vitreous body showing felt-work of fibres hidea, the continuation of the central 



and atrophic traces of cells. X 450. (Retzius.) . . . 



artery of the retina, which passes to 



the lens and assists in forming the embryonal vascular envelope surrounding the lens. 

 Usually the embryonal connective tissue, together with the blood-vessel, disappears ; 

 occasionally, however, delicate remnants of this tissue can be detected. 



The normal adult vitreous ordinarily contains no cells, but some are occasionally 

 seen near the surface, beneath or on the hyaloid membrane. They are amoeboid, 

 often contain vacuoles and are to be considered as modified leucocytes. In addition 

 a few branched connective-tissue cells may be present. 



Practical Considerations. Congential abnormalities of the vitreous arc due 

 either to a persistence of some part of its foetal vascular apparatus or to an atypical 

 development of the tissue from which it is formed. The remains of these structures 

 may occasionally be seen as a filamentous band, free at one end, which floats in the 

 vitreous, the other end being attached to the optic disc behind, or the posterior sur- 

 face of the lens in front. The strand may be attached at both ends, with or without 

 a patent artery. Small rounded gray bodies, apparently cystic and attached to the 

 disc, are occasionally seen. They are in some way the remains of the fcetal vascular 

 apparatus. The congenital opacities sometimes seen at the posterior pole of the lens 

 are probably derived from the posterior fibro-vascular sheath of the lens. Materials 

 from the blood are readily absorbed by the vitreous, as the bile in jaundice. 



Muscte volitantes are the flocculi, seen by the patient as black spots 

 fore the eyes, and are sometimes made up of inflammatory exudate from inflam- 

 mation of the internal or middle coat of the eye. They may be due to blood from 

 traumatic or spontaneous hemorrhage into the vitreous. Muscat volitantes are often 

 seen independently of any vitreous disease and are due to the shadows thrown upon 

 the retina by naturally formed elements in the vitreous body, perhaps the remains 

 of embryonic tissue. Some of the vitreous may be lost and rapidly replaced with- 

 out seriously disturbing sight. In the removal of cataract, the suspensory ligament 

 may be divided and an embarrassing loss of vitreous may result. 



A foreign body in the vitreous chamber generally gives rise to a serious inflam- 

 mation, which may destroy the eye. If loose, it tends by gravity to settle in tin- 

 lower portion, and usually rests on the posterior part of the ciliary body (T. Collins). 

 Rarely, in the absence of infection, it has remained for years without setting up 

 inflammation. The rule is, however, to remove them, when recent, as early as 

 possible, as inflammation may set in at any time. In most cases the foreign body 



lals 



be- 



im. 





