THE OCULAR CONTENTS 669 



THE VITREOUS HUMOR 



The vitreous humor (vitreous body) is a soft jelly-like mass which 

 fills the entire cavity of the eye behind the line of the ora serrata and 

 crystalline lens. About 98 per cent, of its composition is water. It is 

 completely invested by the hyaloid membrane. Its anterior excavation 

 which holds the posterior convexity of the lens is known as the hyaloid 

 or patellar fossa. The vitreous humor appears to be a peculiarly deli- 

 cate form of very loose gelatinous connective tissue whose scanty fibers 

 present a somewhat concentrically lamellated arrangement and are so 

 very delicate as to be recognized under ordinary conditions only with the 

 greatest difficulty. 



Occasionally stellate and fusiform cells, remarkable for their large 

 vacuoles and varicose processes, have been demonstrated in small num- 

 bers within the vitreous body. Small rounded cells somewhat resembling 

 leukocytes are also found, but for the most part they are flattened against 

 the hyaloid membrane; they occur in very limited numbers. 



These various cells, as well as occasional filamentous remnants of 

 the original mesenchymal constituents of the vitreous humor, may cast 

 shadows upon the retina within the visual field. Such shadows, called 

 rmiscce volitantes, on account of their 'flitting* motion when the eyes 

 are moved, are seen when looking at a bright light, or frequently in 

 looking through the microscope. In advanced age crystals may form 

 in the vitreous which are observed to settle to the bottom of the eye 

 when the eyes are held still. 



THE HYALOID MEMBRANE 



The hyaloid membrane is a very thin structure which surrounds the 

 vitreous humor and unites it to the inner surface of the retina and the 

 crystalline lens. It consists of delicate glassy fibers so disposed as to 

 form an extremely thin reticular membrane. It passes forward over the 

 inner surface of the retina, to which it is loosely united, until at the ora 

 serrata its fibers leave the retinal surface and pass inward to the margin 

 of the lens to become inserted into the lenticular capsule. 



THE SUSPENSORY LIGAMENT 

 (Zonula Ciliaris) 



Certain fibers from the hyaloid membrane pass forward from the 

 ora serrata and are firmly adherent to the ciliary processes, or become 



