THE EYE 1517 



ophthalmic or first division of the fifth cranial nerve. They 

 are about sixteen in number, and pierce the back part of the 

 sclerotic around the optic nerve. They then pass forwards between 

 the sclerotic and choroid, giving branches to the latter coat, which 

 become disposed in a plexiform manner amongst the bloodvessels. 

 Having reached the comeo-scleral junction, the nerves enter the 

 ciliary muscle, in which they form a plexus. From this plexus 

 branches enter the iris at the ciliary margin. These branches 

 accompany the vessels, and, by their subdivisions and communi- 

 cations, they form a copious plexus of non-medullated fibres in the 

 connective -tissue stroma of the iris. The sphincter pupillse is sup- 

 plied by fibres which are derived from the oculo-motor or third 



Pupil 



ins 



..Ciliarj- Muscle 



Ciliary Nerves ^-- "^^i^^B^P Vena Vorticosa 



Optic Nerve and Ciliary Nerves. --^H ' Portion of Sclerotic 



Fig. 631. — The Choroid and Iris, showing the Ven^ Vorticos.e 

 AND Ciliary Nerves (after Hirschfeld and Leveille). 



(The Sclerotic and Cornea have been removed). 



cranial nerve, through means of the motor root of the ciliary 

 ganglion. The dilator pupillae is supplied by fibres which are 

 derived from the sympathetic through means of the sympathetic 

 root of the ciliary ganglion. 



Membrana Pupillaris. — During intra-uterine life the pupil is closed by a 

 delicate membrane, called the membrana pupillaris. This membrane is vas- 

 cular, except at its centre, the arteries being derived from the cu-culus minor, 

 and from those of the front part of the capsule of the crystalline lens. The 

 vessels converge from the circumference of the membrane to near its centre, 

 and terminate by forming loops. 



The membrana pupillaxis disappears shortly before birth. 



Internal Coat. 



Retina. — ^The retina is the internal or nervous tunic of the eye- 

 ball. It is soft in consistence, translucent, and of a pinkish colour. 

 Its mtemal surface is in contact with the hyaloid membrane, 



