378 ANATOMY IN A NUTSHELL. 



10. Pigmentary Layer. 



The refracting media are (1) Aqueous humor, (2) Vitreous humor, and 

 (3) Crystalline lens. 



The capsule of Tenon is a layer of fascia which surrounds the posterior 

 five-sixths of the eve-hall. Where the optic nerve enters it is continuous with 

 the sclerotic coat. Anterior it is connected loosely to the sclerotic at the 

 corneo-sclerotic junction. It is pierced by the tendons of the four Recti and 

 two Oblique muscles of the eye. Between the anterior and posterior attach- 

 ments there is a delicate attachment, between the capsule and the eye-ball, of 

 connective tissue; these constitute extensively lymphatic spaces in which the 

 eve-ball glidesjthis is a ball-and-socket (enarthrodial) joint. An expansion from 

 the sheath of the Superior oblique muscle blends with the tendon of the Levator 

 palpebrse. An expansion from the Inferior rectus is attached to the inferior 

 tarsal plate, therefore these two Recti muscles influence the movements of the 

 evelids. The expansion of the sheath of the Internal rectus is attached to the 

 lachrymal bone and is called the internal check ligament. The expansion from 

 the External retcus which is very strong, is attached to the malar bone and is 

 called the external check ligament. The suspensory ligament of the eye is at- 

 tached to the malar and lachrymal bones, passing below the eye-ball ;it is narrow 

 at each extremity and broad in the center. The anterior pole is the central 

 point of the anterior curvature of the eye-ball ;the posterior pole is the central 

 point of the posterior curvature. The sagittal axis is a line joining these two 

 poles. The transverse diameter of the eyeball is about one inch, the verti- 

 cal nine-tenths, and the antero-posterior is intermediate. 



The sclerotic coat is fibrous and opaque tunic, occupying the posterior five- 

 sixths of the eye-ball. It is continuous in front with the cornea. The outer 

 surface is white, being covered with conjunctiva. It is smooth, except where 

 the muscles are inserted. Its inner surface is brown and marked by grooves 

 for the ciliary vessels and nerves and is loosely connected to the outer surface 

 of the choroid by fine cellular tissue (lamina fusca) thus forming the perichoroi- 

 deal lymphatic spaces. The optic nerve passes through the posterior part of 

 the sclerotic coat about one-eighth of an inch internal to the axis of the eye-ball. 



The point of perforation is called the lamina cribrosa. The outer sheath of 

 the optic nerve blends with the sclerotic coat at its entrance. The sclerotic is 

 thickest at the posterior part of and thinnest about one-fourth an inch from the 

 cornea. The canal of Schlemm, or sinus venosus scleroe, is close to the junction 

 of the cornea with the sclerotic; ii is a snail circumferential lymphatic space. 

 The structure of the sclerotic is white fibrous tissue intermingled with elastic 

 tissue and flattened connective tissue corpuscles which are contained in the cell 

 between the fibers. Some of the corpuscles are pigmented. 



The nerves are from the ciliary, but their mode of ending is not known. 

 The vessels are from the short and anterior ciliary arteries of the ophthalmic. 



The cornea is transparent and forms about one-sixth of the circumference 

 of the eye-ball anteriorly. It is a segment of a smaller sphere than that which 

 forms the posterior five-sixths. It fits into the sclerotic coat somewhat like 

 a watch crystal fits into the face of a watch, thus projecting beyond the curva- 



