46 SURGICAL APPLIED ANATOMY. [Chap. iv. 



nearly parallel to one another, are very closely set, 

 and do not move with the conjunctiva. This zone is 

 known as the zone of ciliary congestion, or the circum- 

 corneal zone. 



4. The vessels of the conjunctiva are derived from 

 "the lachrymal and two palpebral arteries. These 

 vessels, in cases of inflammation, are readily dis- 

 tinguished from those last described. They are of 

 comparatively large size, are tortuous, are of a bright 

 brick-red colour, can be easily moved with the con- 

 junctiva, and as easily emptied of their blood by 

 pressure. The differences presented by these two 

 sets of vessels serve in one way to distinguish in- 

 flammation of the conjunctiva from that involving 

 deeper parts. The conjunctival vessels around the 

 margin of the cornea form a closer plexus of anasto- 

 mosing capillary loops, which become congested in 

 severe superficial inflammation of the cornea, and 

 may then form a zone around the margin of the 

 cornea, which can, however, be distinguished from 

 the " ciliary zone " by the general characters just 

 named. The retina has a vascular system of its own, 

 supplied through the arteria centralis retince, which is 

 nowhere in direct communication with the choroidal 

 vessels, except just at the entrance of the optic nerve. 

 Indeed, the outer layers of the retina which are in 

 relation with the choroid coat are entirely destitute of 

 vessels. Thus, when the central artery of the retina 

 becomes plugged, sudden blindness follows, and as the 

 meagre collateral circulation that is established by the 

 minute anastomoses about the entrance of the nerve 

 is quite insufficient, the retina soon becomes oedema- 

 tous and inflamed. A permanent plugging of the 

 central artery means, therefore, a practical extinction 

 of the vascular system of the retina. 



In cases of haemorrhage between the choroid and 

 retina the blood must come from the choroidal vessels ; 



