THE SYMPATHETIC SYSTEM. 499 



aorta, are distributed to the stomach, intestine, spleen, pancreas, liver, 

 kidneys, supra-renal capsules, and internal organs of generation. 



In the pelvis, there are four or five pairs of ganglia, situated on the 

 anterior aspect of the sacrum, and, at its lower extremity, the " gan- 

 glion impar," which is regarded as a fusion of two symmetrical ganglia. 



In all these parts a main characteristic of the sympathetic nerves is 

 their arrangement in the form of plexuses, which surround the arterial 

 branches, and follow their peripheral distribution in the vascular organs. 



Sensibility and Motor Power in the Sympathetic System. 



The sympathetic ganglia and nerves are endowed both with sensi- 

 bility and the power of exciting motion ; but these properties are less 

 active than in the cerebro-spinal system, and are exercised in a different 

 manner. If a motor or sensitive spinal nerve be irritated by the 

 galvanic current, the evidences of pain or of muscular reaction are 

 decisive and instantaneous. There is hardly an appreciable interval 

 between the application of the stimulus and the sensation or motion 

 which results. But in experiments on the sympathetic nerves, evi- 

 dences of sensibility, when manifested, are much less acute, and show 

 themselves only after prolonged application of the exciting cause. 



The same character is exhibited in their motor action. If the semilunar 

 ganglion or its nerves be galvanized, no immediate effect is visible ; but 

 after a few seconds a slow, progressive, vermicular contraction takes 

 place in the intestine, and continues for some time after the galvaniza- 

 tion has ceased. 



Connection with the Special Senses. In the head, the sympathetic has 

 an important connection with the special senses. This is especially 

 noticeable in the eye, from influences regulating the movements of 

 the pupil. The reflex action, by which these movements take place, 

 is transmitted by the oculomotorius nerve to the ophthalmic ganglion, 

 and thence by the ciliary nerves to the muscular fibres of the iris. 



The movements of the iris exhibit consequently a somewhat slug- 

 gish character, which indicates the intervention of the sympathetic 

 system. They do not take place instantaneously with the variation 

 of light, but require an appreciable interval of time If both eyes be 

 closed and covered, long enough to allow complete dilatation of the 

 pupils, and then suddenly opened, the pupils contract somewhat rap- 

 idly to a certain extent, and afterward continue to diminish for several 

 seconds, until equilibrium is fairly established. 



As the movements of the iris derive their stimulus, through the 

 ophthalmic ganglion, from the oculomotorius nerve, if this nerve be 

 divided between the brain and the eyeball, the pupil becomes sensibly 

 dilated, and loses in great measure its power of contraction under the 

 influence of light. There is a partial paralysis, in which the circular 

 fibres of the iris are relaxed, while its radiating fibres continue to act, 

 causing enlargement of the pupil. 



On the other hand, if the sympathetic nerve be divided in the neck, 



