814 



THE OEGANS OF SENSE. 



Veins of chorioid 



Aperture of 

 pupil 



Long 



ciliary 



artery 



Long 

 ciliary 

 artery 



towards the ciliary margin of the iris, and communicate with the veins of the 

 ciliary processes and with the sinus venosus sclerse. The convergence of the blood- 



vessels towards the aper- 



Auterior ciliary arteries ture Q f t h e pupil gives to 



the anterior surface of the 

 iris a striated appearance. 



The non-striped muscular 

 fibres of the iris are arranged 

 in two sets : (a) circular, 

 (6) radial. The circular 

 fibres form a band, the m. 

 sphincter pupillse, around 

 the pupillary aperture ; by 

 the contraction of these 

 fibres the size of the pupil 

 is lessened. The radial fibres 

 constitute the m. dilatator 

 pupillae and extend out- 

 wards from the sphincter to 

 the ciliary margin. Many 

 anatomists regard the radial 

 fibres, in man and most 

 mammals, as being elastic 



-, , , j 



animals in which the radial 

 fibres are muscular, the 



degree of their development varies considerably ; they are feebly marked in the 



rabbit, but are well developed in the bird, and still more so in the otter. 



The nerves of the chorioid and iris (Fig. 685) are derived from the long and 



short ciliary nerves. The former, two or three in number, are branches of the naso- 



ciliary nerve ; the latter, vary- 



ing from eight to fourteen, 



are derived from the ciliary 



ganglion. Piercing the sclera 



around the. entrance of the 



optic nerve, the ciliary nerves 



traverse the perichorioidal 



lymph space, where they form 



a plexus, rich in nerve-cells, Vena vorticosa 



from which filaments are sup- 



plied to the blood-vessels of 



the chorioid. In front of the 



ciliary muscle a second plexus, 



also rich in nerve -cells, is 



formed ; this supplies the 



ciliary muscle and sends fila- 



ments into the iris, as far as 



its pupillary margin, for the 



supply of its muscular fibres and blood-vessels. The sphincter pupillse is suppliec 



by the oculo-motor nerve, the dilatator pupillse by the sympathetic. 



Anterior ciliary arteries 



FIG. 684. BLOOD-VESSELS OF IRIS AND ANTERIOR PART OF CHORIOID, 

 viewed from the front (Arnold). 



Cornea 



Sinus venosus sclerse - 



Anterior ciliary 

 artery 



Sclera 



Pupil 



Anterior ciliar 

 artery 



Ciliary muscle 



Long posterior 

 ciliary artery 



Vena vortico 



Long posterior 

 ciliary artery 



FIG. 685. DISSECTION OF THE EYEBALL SHOWING THE VASCULAR 

 TUNIC AND THE ARRANGEMENT OF THE CILIARY NERVES AND 



VESSELS. 



RETINA. 



The retina, or nervous tunic of the eyeball, is a soft, delicate membrane, in 

 which the fibres of the optic nerve are spread out. It consists of two strata, viz. 

 (a) an outer, pigmented layer, attached to the chorioid ; and (&) an inner nervous 

 lamina, the retina proper, in contact with the hyaloid membrane of the vitreous 

 body, but attached to it only around the entrance of the optic nerve and in the 

 region of the ciliary processes. Expanding from the entrance of the optic nerve 



