THE EYE. 



335 



This pigment pervades the whole of the choroid, but is 

 found to be more abundant on its internal, than on its ex- 

 ternal surface ; and more abundant and of a deeper color, 

 posteriorly and anteriorly, than laterally. The sclerotic is 

 stained by the pigment. It is of deeper color in the child, 

 and paler and less in quantity in the old. It is entirely 

 wanting in Albinos, and vision is in consequence defective. 

 This pigment is wanting in the bottom of the eye of 

 many of the inferior animals, as the sheep, ox, &c., and in 

 place of it there is seen a beautiful, shining, metallic sur- 

 face called tapetum. The use of the pigment is to darken 

 the interior of the eye, to absorb the superfluous rays of 

 light, and prevent their being reflected back upon the ret- 

 ina. For the same reason the interior of the telescope is 

 blackened. 



There are other parts however, besides the choroid, which 

 have this black pigment, and which being also in close con- 

 nection with it, will now be noticed. These are the ciliary 

 processes and iris, (Fig. 99.) 



FlG - " There is a circular band about 



a line and a half broad, called 

 the ciliary ligament, (Fig. 98, B,) 

 which serves to connect togeth- 

 er the sclerotica, cornea, cho- 

 roid, and iris. It is of a fibro- 

 cellular structure, soft, of a 

 grayish white color, and not 

 blackened by the pigment. 

 The ciliary arteries and nerves 

 enter this ligament, and are 

 traced through it to the iris. From the nerves which Soem- 

 mering saw it contain, he considered it a nervous ganglion. 

 It has also been considered a muscular, tendinous, and 

 glandular structure. A small canal is seen within this lig- 

 ament, called after its discoverer, the canal of Fontana. 



FIG. 99 represents a transverse section of the globe of the Eye seen from 

 within, o Cut edge of the three tunics of the eye. 6 Pupil, c Iris, d Ciliary 

 processes, e Front border of the retina. , 



