T TEGUMENT 



I 



region this sinus presents the appearance of a cleft, the outer wall of which consists 

 of the firm tissue of the sclera, while its inner wall is formed by a triangular mass 

 of trabecular tissue (Fig. 870); the apex of the mass is directed forward and is con- 

 tinuous with the posterior elastic lamina of the cornea. The sinus is lined by 

 endothelium and communicates externally with the anterior ciliary veins. 



The aqueous humor drains into the scleral sinuses by passage through the 

 "pectinate villi" which are analogous in structure and function to the arachnoid 

 villi of the cerebral meninges. 1 



Sulcus circularis cornece 

 Posterior chamber 



Conjunctiva 



Sulcus circularis cornece 

 Ciliary body 



Rectus 

 lateralis 



Hyaloid canal 



Rectus 

 medial is 



Sclera 



Choroid 



Retina 



Fovea centralis 



Nerve sheath 



A. centralis retinae 

 Optic nerve 



erve seat 



Fio. 869. Horizontal section of the eyeball. 



Structure. The sclera is formed of white fibrous tissue intermixed with fine elastic fibers; 

 flattened connective-tissue corpuscles, some of which are pigmented, are contained in cell spaces 

 between the fibers. The fibers are aggregated into bundles, which are arranged chiefly in a 

 longitudinal direction. Its vessels are not numerous, the capillaries being of small size, uniting 

 at long and wide intervals. Its nerves are derived from the ciliary nerves, but their exact mode 

 of ending is not known. 



The Cornea. The cornea is the projecting transparent part of the external tunic, 

 and forms the anterior sixth of the surface of the bulb ; It is almost circular in 

 outline, occasionally a little broader in the transverse than in the vertical direction. 

 It is convex anteriorly and projects like a dome in front of the sclera. Its degree 

 of curvature varies in different individuals, and in the same individual at different 

 periods of life, being more pronounced in youth than in advanced life. The cornea 

 is dense and of uniform thickness throughout; its posterior surface is perfectly 

 circular in outline, and exceeds the anterior surface slightly in diameter. Imme- 

 diately in front of the sclero-corneal junction the cornea bulges inward as a thickened 

 rim, and behind this there is a distinct furrow between the attachment of the iris 

 and the sclero-corneal junction. This furrow has been named by Arthur Thomson 2 



1 Wegefarth, Jour. Med. Research, September, 1914. 



2 Atlas of the Eye, Clarendon Press, Oxford, 1912. 



