ANIMAL MECHANISM. 1 17 



a The optic nerve. 



b The sclerotic coat turned back, so as to show the vessels of the 

 choroid coat. 



ce The ciliary nerves, seen piercing the sclerotic coat, and pass- 

 ing forward to be distributed to the iris. The iris, so highly 

 organized, is not supplied by any nervous influence from the optic, 

 but by the hair-Jike nerves, here displayed, creeping to its map- 

 gin between the two exterior coats. 



d A small nerve passing from the same source to the same termi- 

 nation, but giving off no visible branches. 



ee Two vena vorticosce, or whirling veins, so denominated, because 

 they seem to fall into shapes, resembling falling jets of water ; 

 these return the blood from the eye, sent in by its central and 

 other arteries. 



/ A point of the sclerotic^ through which the trunk of one of the 

 veins has passed. 



A lesser vein. 



The point, or circular point of union, where all the coats of the 

 eye, together with the cornea and iris, seem to be glued firmly 

 together. 



t The iris. 



A; The straight fibres of the iris. 



I A circle of fibres or vessels, which divide the iris into the larger 



circle /,: and the lesser one m. 

 m This letter points to the lesser circle of the iris, 

 n The fibres of the lesser circle, 

 G The pupil. 



PIGMENTUM NIGRUM.* 



Lastly, to complete the internal structure, and fit it for 

 the performance of its destined office, the inside surface 

 of the second coat, choroides, is thoroughly painted black. 

 In the order of explanation, thjs paint is just behind the 

 retina. When the humors have been taken out the pig- 

 ment is readily examined. The use of it is very obvious; 

 viz., to absorb any aberrating or unnecessary rays of 

 light, which confuse the vision ; or destroy the intensity 

 of the impression on the nervous expansion of the retina, 

 and indeed, to suffocate them entirely. 



JUNICA CONJUNCTIVA. 



Posteriorly, the eye, by its long cord of optic nerve, 

 seems to rest on one extremity of an axle ; the opposite 

 in front, being the skin, passing over the eye, as it conies 



*Pigmentum Nigrum black paint 



