200 VISCERAL ANATOMY. 



ceedingly elastic, and curls up inwardly upon itself, when detached from 

 the true cornea. At the corneal margin it breaks up into fibres, which are 

 continuous with the ligamentum pectinatum of the iris. 

 Posterior Epithelial Layer, a single layer of flattened, polygonal, trans- 

 parent, nucleated cells, forming the endothelium of the membrane of 

 Descemet or Demours, and the epithelial lining of the aqueous chamber. 



THE UVEAL TRACT. 



Describe the Choroid. It is the posterior portion of the middle tunic of 

 the eyeball, ^\- to y^ inch thick, and extends from the optic nerve entrance 

 to the ora serrata, a little in front of the equator. It is highly vascular, of 

 dark-brown color, connected to the sclerotic by the Lamina Fusca, terminates 

 anteriorly in the Ciliary Processes, and is composed of four layers, as follows : 

 Tunica Vasculosa, externally, consists of the venae vorticosae and the 



larger arterial branches. . 

 Membrana Ruyschiana, or Chorio-capillaris, the middle layer consists of 



a fine capillary plexus, formed by the short ciliary vessels. 

 Limiting Membrane, a structureless hyaline membrane, covering the inner 



surface of the capillary layer. 



Pigmentary Layer, internally, a single layer of hexagonal nucleated cells, 



loaded with pigment of a brown black color, which is absent in albinos, 



and of slight amount in blondes. [Considered by many anatomists the 



loth layer of the retina.] 



Arteries of the Choroid, are the short posterior ciliary, and recurrent branches 



from the long posterior and anterior ciliary. (See p. 105.) 

 Veins,* unite into 4 or 6 Venae Vorticosae, 4 which pass out through the 



sclerotic near its equator. 



Nerves,* derived from 3d, 5th, and sympathetic, through the long and short 

 ciliary nerves. (See p. 137.) 



What are the Ciliary Processes ? They are 70 or 80 folds, formed by 

 the anterior prolongation of the middle and internal layers of the choroid on 

 the inner surface of the ciliary muscle, being received into corresponding folds 

 on the suspensory ligament of the lens. They are about -^ inch in length, 

 and form a curtain-like expansion behind the iris. 



Describe the Ciliary Body. 5 It is the portion of the uveal tract between 

 the choroid and the iris, 6 and consists of ciliary muscle covered by choroidal 

 stroma and the ciliary processes. The 



Ciliary Muscle or Muscle of Bowman, is a ring of involuntary muscular 

 fibres, supplied by the 3d nerve ; is thickest anteriorly, thin posteriorly. 

 Its fibres arise from the corneo-sclerotic junction, and pass backwards to 



