198 VETERINARY PHYSIOLOGY 



The interruption of fibres in ganglia, or their passage 

 through these structures, has been detennined by taking 

 advantage of the fact that nicotine, in one per cent, solution 

 when painted on a ganglion, poisons the synapses but does 

 not influence the fibres. Hence, if when a ganglion is painted 

 with nicotine, stimulation of the fibres on its proximal 

 side produces an effect, it is proved that the break is not in 

 that ganglion. 



The Visceral Nerves may be divided into two sets — 



I. The Thoracico-Abdominal or True Sympathetic Fibres, which 

 come out in the middle region of the spinal cord and jiass 

 through the lateral ganglia of the sympathetic chain (fig. 99). 

 They are distributed to the — 



(1) Head and Neck. — These leave the spinal cord by 

 the upper five dorsal nerves and pass upwards in the 

 sympathetic cord of the neck to the superior cervical 

 ganglion where they have their cell stations. From these, 

 fibres are distributed to the parts supplied. Stimulation of 

 these fibres causes — l.s^, Vaso-constriction of the vessels of 

 the face and head ; 2nd, Dilatation of the pupil (see p. 148) ; 

 Srd, Prominence of the eyeball, due probably to the stimula- 

 tion of visceral muscular fibres in the eyelids by which these 

 are drawn apart and the eye exposed and allowed to bulge 

 forward ; 4!th, Secretion of the salivary, lachrymal, and 

 sweat glands. 



(2j Thorax. — The fibres to the thoracic organs also 

 come off in the upper dorsal nerves. They have their cell 

 stations in the stellate ganglion in the dog, and pass to the 

 heart and lungs. 



(3) Abdomen. — These fibres come off in the lower 

 dorsal and upper lumbar nerves. They course through 

 the lateral ganglia and form synapses in the collateral 

 ganglia of the abdomen — the solar plexus and the superior 

 and inferior mesenteric ganglia. From these, they are 

 distributed to the abdominal organs, being vaso-constrictor 

 to the vessels, and inhibitory to the muscles of the stomach 

 and intestine. 



(4) Pelvis. — The fibres for the pelvis leave the cord by 

 the lower dorsal and upper lumbar nerves, and have 



