420 NORMAL HISTOLOGY AND ORGANOGRAPHY. 



surface, and also forms a lining membrane against 

 which the pigment cells of the retina are applied. 



2. The Ciliary Body. The ciliary body is that por- 

 tion of the tunica media extending between the ora 

 serrata of the retina and the base of the iris. On the 

 inner surface of this body there are about seventy 

 meridional folds called the ciliary processes. Second- 

 ary folds and processes appear on and between the 

 primary folds, while the whole surface is clothed 

 with two rows of epithelial cells, the pars ciliaris 

 retina. Of these the outer layer is deeply pig- 

 mented and represents the outer layer of the second- 

 ary optic vesicle, while the inner layer is non- 

 pigmented and develops from the inner layer of the 

 optic vesicle. The greater bulk of the ciliary body 

 is made up of smooth muscle tissue called the ciliary 

 muscle, or muscle of accommodation. This muscle 

 may be divided into three portions. The outer por- 

 tion is made up of meridional fibers. The middle 

 division of radial fibers have their origin near the 

 canal of Schlemm, from which they spread out like 

 a fan. The inner portion is near the base of the iris 

 and the fibers are circular. The combined action of 

 these fibers is to pull the choroid coat forward and 

 inward and thus slacken the tension on the suspen- 

 sory ligament of the lens, as this ligament joins with 

 the epithelial cells of the ciliary body as well as with 

 the hyaloid membrane that encloses the vitreous 

 humor. Under this condition the lens becomes 

 more convex and the eye is focused to near objects. 



3. The Iris. The iris is a pigmented circular cur- 

 tain that occludes the rays of light from the periphery 



