ACTION OF THE SYMPATHETIC ON THE VESSELS. 307 



The lenticular ganglion of the orbit, is the centre which governs the 

 nutrition of the eyeball, and through which the movements of the iris 

 are accomplished; the sensory nerves of the eyeball, coming from the 

 first division of the fifth, and the motor nerves from the third cranial 

 nerve, pass through it, as elsewhere explained. The relative size of 

 this ganglion, in animals, is proportionate to the activity of the iris, 

 and to the general powers of sight; it is large in nocturnal animals. 



Division of the sympathetic branch which connects the lenticular 

 ganglion of the orbit with the superior cervical ganglion, causes imme- 

 diate paralysis of the radiating fibres of the iris; and the pupil con- 

 tracts, in consequence of the action of the circular fibres, which are 

 governed through the oculo-motor nerve of the eye. On the other 

 hand, galvanic irritation of the lenticular ganglion, or of the cervical 

 or dorsal portion of the spinal cord, with which the upper cervical gan- 

 glion of the sympathetic is connected (provided, in the latter cases, 

 that the shocks are sufficiently powerful), is followed by contraction 

 of the radial fibres, and consequent dilatation of the pupil. Irritation 

 of the cervical portion of the cord, produces protrusion of the eyeball; 

 whilst section of the same, causes its retraction, and also gives rise to 

 partial closure of the eyelids, to a forward movement of the nictitating 

 membrane, and to a narrowing of the nasal and buccal openings; irri- 

 tation produces the opposite eifects. 



Irritation of the nerves of the heart, affects the movements of that 

 organ. Galvanism, applied to the cervical part of the sympathetic, to 

 the superior thoracic ganglion, to the branches connecting it with the 

 spinal cord, or to the cervical portion of the latter, determines a re- 

 markable acceleration of the heart's beats ; in the two latter cases, in 

 a less marked manner. The diminution in frequency of the action of 

 the heart, by a weak stimulation, and its complete arrest, by a strong 

 stimulation of the vagi nerves, have already been mentioned, as well 

 as the weakening effect of removal of the cerebro-spinal axis. The 

 pulsations themselves seem, therefore,, to be determined by some in- 

 fluence emanating from the sympathetic nerve y but their force is gov- 

 erned by the cerebro-spinal axis. 



In the same manner, irritatio-n of the splanchnic nerves, of the 

 thoracic portion of the sympathetic, or of the dorsal region of the 

 spinal cord, causes movements in the intestines^ ureters, and bladder; 

 but very strong galvanic shocks diminish the intestinal peristaltic 

 action. 



These movements, even when excited by stimuli applied close to the 

 ganglionic centre, and performed by parts near this centre, always 

 occur slowly, and not instantaneously and spasmodically, as is the case 

 with movements excited through the eerebro-spinal nervous system ; 

 they are more or less rhythmical, continuing to be performed, for some 

 little time, at regular periods of succession, and passing off slowly. 

 When these movements become languid, or even have altogether 

 stopped, they may be increased in activity, or entirely revived, by 

 the fresh irritation of the sympathetic ganglia or nerves. These pe- 

 culiarities of the reflex actions of the sympathetic, have been attrib- 



