^454 



HUMAN ANATOMY. 



irritating conditions a superficial inflammation may develop, covering the cornea with 

 a new vascular tissue (pannusj, the deeper layers still being bloodless. Owing to a 

 very free nerve-supply the cornea is very sensitive. 



As in the sclera, weakness of the cornea leads to bulging, from internal pressure. 

 The causes of weakness may be congenital and acquired. Congenital co?iical cornea 

 or kerataconus may occur, and it is believed that some congenital defect predisposes 

 to the same condition that occurs in the adult. It is not due to weakening from pre- 

 vious ulceration or injury of the cornea, and the exact cause is not known. 



A staphyloma of the cornea is a similar condition in which the protuberance is 

 due to the distention of a cicatrix, to the posterior surface of which the iris may be 

 attached (anterior synechiae of the iris). The cicatrix involves all the layers of the 

 cornea, and is the result of a perforating ulcer. If the ulcer had been a non-per- 

 forating one, and the iris did not adhere to its posterior surface, the protrusion of the 

 cornea would then be called a keratectasia. 



If all the layers of the cornea to the posterior elastic lamina had been destroyed 

 by the ulcer, and this layer had bulged through the weakened spot like a hernial 

 pouch it would be called a keratocele. 



Arcus senilis is usually a sign of old age. Modern investigation indicates that it 

 is due to a fatty degeneration of the substantia propria, the exact nature of the fatty 

 material being unknown. It first appears as a crescent above, then below, and finally 

 a complete circle is formed. It never interferes with sight. It is occasionally seen 

 in children. 



The Vascular Tunic. 



The middle or vascular coat of the eye (tunica vasculosa oculi), or uveal tract, 

 consists of a vascular connective tissue sheath, which lies internal to the outer fibrous 



Fig. ]2o8. 



Anterior chamber 



Pupil 



Circulus arteriosus minor 



Artery joining ring 



Vena vorticosa 



Short post, ciliary 

 artery 



Cornea 



Iris 



Circulus arteriosus major 



^~ Anterior ciliary artery 



Ciliary ners'es 



Venous whorl 



Ciliary nerve 

 Long posterior ciliary artery 



Optic nerve 



s 



Sclera 



Injected eyeball, showing arrangement of ciliary arteries and of choroidal veins. X 3. 



preparation made by Professor Keiller. 



Drawn from 



tunic. It extends from the entrance of the optic nerve to the pupil and includes 

 three portions, which from behind forward are the choroid, the ciliary body and the 

 %fis. The choroid and ciliary body are in contact with the sclera, but the iris bends 



