258 CIRCULATION OF THE BLOOD. 



integument of the head, must reach their destination by pass- 

 ing through the superior cervical ganglion. As, however, the 

 superior ganglion is also in direct communication with the 

 spinal cord, the vascular paralysis is incomplete unless this 

 communication is broken by the extirpation of the ganglion. 

 To accomplish this, the incision must be continued upwards 

 in the angle of the jaw (see fig. 227). The carotid artery and 

 the vagus which accompanies it, having been brought into 

 view as far upwards as the stylohyoid muscle, are drawn for- 

 wards and towards the middle line with the blunt hook by an 

 assistant, while the sympathetic trunk is followed upwards 

 behind the artery with the aid of two pairs of blunt forceps. 

 The space in which tin: ganglion lies is crossed by the trunk 

 of the hypoglossal nerve, and by the stylohyoid muscle. The 

 latter should be divided. The extirpation of the ganglion is 

 best effected with blunt-pointed scissors. After section of the 

 sympathetic trunk in the neck, the normal condition of the ear 

 is gradually restored; but if the ganglion is destroyed, the 

 effect is permanent. 



56. (2.) Demonstration of the Vasomotor Functions 

 of the Splanchnic Nerves. The splanchnic nerves con- 

 lain (in addition to those fibres which govern the peristaltic 

 movements of the intestine, with which we have at present no 

 concern) sensory and vasomotor fibres. The vasomotor fibres 

 are distributed to the arteries of the abdominal viscera. Their 

 importance depends on the fact that these arteries receive so 

 larijc a, share of the systemic blood-stream (especiall}' in the 

 rabbit), that the resistance offered by the arterial system to 

 the discharge of blood from the heart is largely affected by 

 any alteration of their calibre. The sensory part of the nerve, 

 in common with other sensory nerves, contains fibres by which 

 the vasomotor centre is influenced. It is also, as will be seen 

 in a future section, in reflex relation with the heart through 

 the vagus. The splanchnic nerve in the rabbit leaves the sympa- 

 thetic trunk at the 8th or 9th ganglion, passes downwards in 

 front of the psoas major muscle, receiving branches from the 

 other thoracic ganglia. At the level of the tenth thoracic 

 vertebra, the two nerves lie on either side of the descending 

 aorta, and accompany it downwards until it reaches the dia- 

 phragm, at which point the right splanchnic is further away 

 from the vessel than the left. After entering the belly, the 

 left splanchnic retains the same relation to the aorta as before, 

 ending in the lower of the two cvt'liac ganglia, which is easily 

 found above the left supra-renal capsule on the front of the 

 aorta. The right nerve is more difficult to find from its lying 

 further from the aorta, separated from it by the breadth of the 

 vena cav.a. It ends at the level of the right supra-renal cap- 

 sule, iu the superior cteliac ganglion which lies in front of the 



