118 TOPOGRAPHICAL ANATOMY OF THE 



veins ami with the anterior chamber of the eyeball, is present near the 

 corueo-scleral junction. 



The cornea^ is transparent, non-vascular, of great density and of 

 ovoid outline, and forms approximately one-fifth of the whole fibrous 

 tunic of the eyeball. Owing to the greater amount of overlap by the 

 sclera above and below, the cornea presents a more markedly ovoid 

 configuration when viewed from the front than it does when seen from 

 behind. The broader end of the outline is medial. 



The curvature of the cornea is different in different directions and 

 in different regions. It is greater in the vertical than in the horizontal 

 direction, and the highest point of the curvature {vertex cornece) is 

 below and medial to the mid-point of the transverse diameter. The 

 anterior surface (facies anterior) is covered by conjunctiva reduced to 

 its epithelial elements only. The posterior surface (facies posterior) is 

 bathed by the aqueous humour of the anterior chamber. 



The cornea contains the following layers : — (1) The anterior epi- 

 thelium, stratified in character and continuous with the conjunctiva; 

 (2) the substantia propria, forming almost the whole of the thickness 

 of the cornea and consisting of lamellae of connective fibres ; (3) the 

 posterior elastic larnina ; and (4) the endothelium of the anterior 

 chamber, a single layer of low, polyhedral cells continued on to the 

 anterior surface of the iris. At the periphery of the cornea the 

 posterior elastic lamina divides into three sets of fibres. The most 

 superficial blend with the sclera ; the middle fibres give attachment 

 to the ciliary muscle ; and the deepest fibres radiate into the iris as 

 the ligamenium pectinatum.^ iridis, between the bundles of which 

 are the spatia anguli iridis that communicate with the anterior 

 chamber of the eyeball and the sinus venosus sclerse.^ 



The choroid^ (chorioidea), a thin, pigmented membrane that lies 

 between the sclera and the retina, forms the greater part of the middle 

 or vascular tunic of the eyeball, and is thickest in the region of the 

 posterior pole and the entrance of the optic nerve. As has been 

 demonstrated by dissection, the connection between the choroid and 

 the sclera is loose, except at the entrance of the optic nerve. In 

 general, the colour of the membrane is a deep brown verging upon 

 black, but if it be viewed from the front, a shining, iridescent, cres- 

 centic or roughly triangular area is conspicuous above the optic papilla. 



^ Corneus [L.], horny. 



2 Fed en [L.], a comb. 



3 The brief details of structure given herein must be amplified by reference to 

 one of the standard textbooks on microscopic anatomv. 



* Chorioideus [L.], xop'-o^'-^s (choriceides) [Gr.], skin-like. Corivm [L.], xopi-o" 

 (chorion), [Gr.], skin. 



