552 



PHYSIOLOGY 



many sensory nerves, and is constantly observed as a result of severe pain. 



The presence or absence of dilated pupils may serve therefore as a means of 



testing how far an emotional expression of pain is to be credited to a physical 



cause. 



(3) The pupils are often dilated in emotional conditions such as fear. 



(4) Dilatation of the pupils occurs 

 in every condition of extreme exhaus- 

 tion, when the activities of the nervous 

 centres are lowered. It is therefore seen 

 during the third stage of chloroform 

 anaesthesia, or in the comatose condi- 

 tion produced by excess of alcohol. 

 Among the drugs which cause dilatation 

 of the pupil the belladonna alkaloids, 

 atropine and homatropine, are the best 

 known. These alkaloids will produce 

 dilatation of the pupil when simply 

 dropped into the conjunctival sac, and 

 are therefore largely used to dilate the 

 pupil as a preliminary to ophthalmo- 

 scopic investigation of the eye. 



INNERVATION OF THE INTRINSIC 



MUSCLES OF THE EYE 

 The eyeball is supplied by the short 

 ciliary nerves, which come from the 

 lenticular or ciliary ganglion and pass- 

 ing forwards pierce the sclerotic coat 

 about half-way between the equator 

 and the posterior pole of the eyeball. 

 The lenticular ganglion has three so- 



l.g, lenticular ganglion with its three called ^^ by which it ig connec ted 



with or receives fibres from : 



(1) The third or oculo- motor nerve, 

 by the ' short root.' 



(2) With the sympathetic plexus 

 lying in the cavernous sinus, and, 



through the fibres lying on the internal carotid artery, with the cervical 

 sympathetic nerve. 



(3) With the nasal branch of the ophthalmic division of the fifth nerve by 

 means of the ' long root.' 



The eyeball is also supplied by the two long ciliary nerves (Fig. 278) 

 which come direct from a branch of the ophthalmic division of the fifth 

 nerve and pass forwards on to the eyeball, piercing the sclerotic coat in 

 front of the point at which this coat is penetrated by the short ciliary 

 nerves. There are thus three nerves by means of which the activity of the 



sym 



FIG. 278. Nerve-supply to the eyeball. 

 (After FOSTER.) 



ng 



roots, viz. : r.b, radix brevis or short 

 root ; r.l, radix longus or long root ; 

 sym, sympathetic root ; V. opth. oph- 

 thalmic division of V nerve ; /// oc.m, 

 oculo -motor nerve ; //, optic nerve ; l.c, 

 long ciliary nerves ; s.c, short ciliary 

 nerves. 



