236 NORMAL HISTOLOGY. 



and attached posteriorly to the choroid, is a muscle 

 having the form of a flattened ring, thickest in front, 

 called the ciliary muscle. The direction of the 

 muscle-cells in the ciliary muscle, which are of the 

 smooth variety, is in part meridional or oblique, in 

 part circular. The ciliary processes and muscle 

 form together the greater part of a structure known 

 as the ciliary body. The retina, the innermost of 

 the layers forming the wall of the eyeball, spreads 

 out from the point of entrance of the optic nerve 

 over the inner surface of the choroid. At about a 

 third of the distance back from the front of the eye, 

 the nerve-elements of the retina cease in a wavy line, 

 called the ora serrata ; certain cellular elements 

 continue, however, over the ciliary processes, under 

 the name of pars ciliaris retina. 



The crystalline lens is suspended close behind the 

 iris by a firm, delicate, fibrillated membrane, called 

 the suspensory ligament, which is attached, on the 

 one hand, to a membrane covering the ciliary pro- 

 cesses, and on the other to the capsule of the lens. 



The cavity of the eyeball is divided by the lens 

 and. its suspensory ligament into two chambers,* 

 the anterior and smaller of which is filled with a 

 homogeneous fluid, the aqueous fluid ; the posterior, 



* By the anterior and posterior chambers of the eye, ophthalmolo- 

 gists at present mean the cavities in front of the lens, separated by 

 the iris, and formerly regarded as constituting the anterior chamber 

 alone, while that containing the vitreous was called the posterior. 



