chap. iv. j THE ORBIT AND EYE. 53 



and is often occupied by opaque bodies of various 

 kinds. Foreign bodies have lodged in the vitreous 

 for considerable periods without causing any symp- 

 toms. The muscse volitantes that so often trouble the 

 myopic are due to little opaque matters in the vitreous, 

 and very often have exactly the appearance that the 

 corpuscles of the vitreous present when seen under the 

 microscope. 



The vitreous is readily separated from the retina 

 except behind, opposite the disc where the artery to 

 the lens enters in the foetus. 



Glaucoma is a disease the symptoms of which 

 are all dependent upon an increase in the intraocular 

 tension of the globe. The increased tension is due 

 to an excess of fluid within the eye-ball, and this would 

 appear to be due to certain changes, seldom absent 

 in the glaucomatous, that interfere with the normal 

 escape of this fluid. Normally there is a constant 

 movement of fluid from the vitreous through the 

 suspensory ligament into the posterior chamber, and 

 thence round the pupillary margin of the iris to the 

 anterior chamber. From the anterior chamber the fluid 

 can escape into the veins through the gaps in the liga- 

 mentum pectinatum already alluded to (Fig. 10). It is 

 remarkable that in nearly every case of glaucoma these 

 gaps are occluded by the complete obliteration of the 

 angle between the periphery of the iris and the cornea, 

 which angle is normally occupied by the ligamentum 

 pectinatum. The relief given to glaucoma by iri- 

 dectomy appears to depend upon the circumstance 

 that the operation practically opens up again these 

 channels of communication from the aqueous, since 

 the procedure, to be successful, should involve an in- 

 cision so far back on the sclerotic as to fully pass 

 through the angle just alluded to. It is needful also 

 that the iris should be removed quite up to its at- 

 tachment, and that the portion resected should be 



