DISSECTING MANUAL. 



ous sinus. Its branches are the arterial venae comites except 

 the frontal, which joins the angular vein. [879] 



THE EYEBALL. 



This is composed of segments of two spheres, the anterior 

 (corneal) being of shorter radius than the posterior (scleral) ; 

 the centres (anterior and posterior poles) of the curvatures are 

 joined by the sagittal axis while the equator is midway be- 

 tween them. [724] 



Outer Coat. The cornea, the anterior sixth, is a transparent 

 laminated structure, covered externally by epithelium con- 

 tinuous with that on the conjunctiva. The sclera, the posterior 

 five-sixths, is an opaque structure; externally it is whitish and 

 separated from the capsule of Tenon by the suprascleral 

 lymphatic space; internally it is brownish and firmly at- 

 tached to the choroid at the entrance of the optic nerve, but 

 only loosely attached elsewhere by a fine meshwork (lamina 

 fusca), being separated from it by a lymph space (spatium 

 perichoroideale). Posteriorly the sclera is pierced (lamina 

 cribrosa) by the optic nerve and ciliary vessels and nerves; 

 just behind its equator are two orifices above, and two below, 

 for veins. A circular canal (Schlemm) lies deeply in the 

 corneo-scleral junction and communicates with the anterior 

 chamber and scleral veins. [725] 



Middle Coat. The choroid is a vascular and dark brown, 

 or black, structure lying between the sclera and retina; it is 

 pierced by the optic nerve and adheres to the retina. The 

 ciliary body, which connects the choroid with the circumfer- 

 ence of the iris, presents the following structures : orbicularis 

 ciliaris, a narrow zone with many ridges, lying next to the 

 choroid; ciliary processes, about seventy radial thickenings; 

 and ciliary muscle, composed of radial fibres externally and 

 circular fibres internally. The iris is a contractile diaphragm 

 which divides the space between the cornea and lens into two 

 parts, the anterior and posterior chambers. It consists of 



[56] 



