138 HUMAN PHYSIOLOGY. 



1. The lamina supra-choroidea. 



2. The elastic layer of Sattler, consisting of two endothelial layers. 



3. The chorio-capillaris, choroid proper, or membrane of Ruysch, a thick 

 elastic network of arterioles and capillaries lying within the outer layer of 

 veins and larger vessels, called the vena vorticosse. 



4. The lamina vitrea, or internal limiting membrane. (The pigmentary 

 layer, formerly classed as belonging to the choroid, is now known to belong, 

 embryologically and physiologically, to the retina.) 



The Function of the Choroid is to provide for the vascular supply 

 and drainage of the body of the eye, and to furnish an uniform and high 

 temperature to the retina. 



FIG. 15. 



SCLEROTIC COAT REMOVED TO SHOW THE CHOROID, CILIARY MUSCLE AND NERVES. 



a. Sclerotic coat. b. Veins of the choroid. c. Ciliary nerves, d. Veins of the choroid. 

 e. Ciliary muscle, f. Iris. (From Holders Anatomy.} 



The Iris is a circular, muscular diaphragm, placed in the anterior por- 

 tion of the eye, and perforated a little to the nasal side of the centre by a 

 circular opening, the pupil; it is attached by its periphery to the point of 

 junction of the sclerotic and cornea. It is composed of a connective- tissue 

 stroma, blood vessels and non-striated muscular fibres, circular and radiat- 

 ing. The circular fibres surround the margin of the pupil like a sphincter, 

 and are controlled by the 3d pair of nerves ; the radiating fibres (dilators 

 of the pupil) radiate from the centre toward its circumference, and are 

 controlled by the sympathetic system of nerves. 



The Ciliary muscle is a grayish circular band, consisting of unstriped 



