THE SENSE OF SIGHT. 



. 



cervical ganglion. They reach the iris by way of the cervical sympa- 

 thetic, the ophthalmic division of the fifth, and the long ciliary nerve. 

 Stimulation of these nerves is followed by dilatation of the pupil. 

 Both the ciliary and superior cervical ganglia are in relation with 

 pre-ganglionic fibers coming from the central nerve system. (See 



Page 535-) . 



The ciliary muscle is a gray circular band about two millimeters 

 in width, consisting of non-striated muscle-fibers. The majority of 

 these fibers pursue a radial or meridional direction. Taking their 

 origin from the junction of the sclera, cornea, and iris, they pass 

 backward to be inserted into the chorioid coat opposite the ciliary 

 processes. The inner portion of the muscle is interrupted by bundles 

 of fibers which pursue a circular direction. They collectively con- 

 stitute the annular or ring muscle of Miiller. The ciliary muscle in 



FIG. 278. SECTION THROUGH THE CILIARY REGION OF THE HUMAN EYE. a. Radi- 

 ating bundles of the ciliary muscle, b. Deeper bundles, c. Circular network. 

 d. Annular muscle of Miiller. e. Tendon of ciliary muscle. /. Muscle-fibers 

 on posterior side of the iris. g. Muscles on the ciliary border of the same. h. 

 Ligamentum pectinatum. (After Iwanoff.') 



common with the circular fibers of the iris receives its nerve-supply 

 direct from the nerve-cells in the ciliary ganglion. Contraction of 

 the ciliary muscle tenses the chorioid coat, and for this reason it is 

 frequently termed the tensor chorioidea. 



The Retina. The retina is the internal coat of the eye, extending 

 forward almost to the ciliary processes, where it terminates in an 

 indented border, known as the ora serrata. In the living condition 

 it is clear, transparent, and pink in color. After death it becomes 

 opaque. The retina is abundantly supplied with blood-vessels, de- 

 rived from the arteria centralis retince, a branch of the ophthalmic, 

 which pierces the optic nerve near the sclera, runs forward in its 

 center, to the retina, in which its terminal branches are distributed. 

 The veins arising from the capillary plexus leave the retina by the 

 same route. 



