CRANIAL NERVES. 195 



plexus; from the various plexuses, nerves follow the gastric, splenic, hepatic, 

 renal, etc., arteries, into the different abdominal viscera. 



The lumbar ganglia, four in number, are placed upon the bodies of the 

 vertebra; they give off branches, which unite to form the aortic lumbar plexus 

 and the hypogastit.plexus, and follow the blood-vessels to their terminations. 



The sacral and coccygeal ganglia send filaments of distribution to all 

 the blood-vessels of the pelvic viscera. 



Properties and Functions. The sympathetic nerve possesses both 

 sensibility and the power of exciting motion, but these properties are much 

 less decided than in the cerebro-spinal system. Division of the sympathetic 

 nerve in the neck is followed by a vascular congestion of the parts above the 

 section on the corresponding side, attended by an increase in the temperature; 

 not only is there an increase in the amount of blood, but the rapidity of the 

 blood current is very much accelerated and the blood in the veins becomes of 

 a brighter color. Galvanization of the upper end of the divided nerve causes 

 all the preceding phenomena to disappear; the congestion decreases, the 

 temperature falls, and the venous blood becomes dark again. 



The sympathetic exerts a similar influence upon the circulation of the 

 limbs and the glandular organs; destruction of the first thoracic ganglion and 

 division of the nerves forming the lumbar and sacral plexuses are followed by 

 a dilatation of the vessels, an increased rapidity of the circulation, and an 

 elevation of temperature in the anterior and posterior limbs; galvanization 

 of the peripheral ends of these nerves causes all of these phenomena to dis- 

 appear. Division of the splanchnic nerve causes a dilatation of the blood- 

 vessels of the intestine. 



These phenomena of the sympathetic nervous system are dependent upon 

 the presence of vaso-motor nerves, which, under normal circumstances, exert 

 a tonic influence upon the blood-vessels. These nerves, derived from the 

 cerebro-spinal system leave the spinal cord by the rami communicantes, 

 enter the sympathetic ganglia around the cells of which they aborize. From 

 these cells new fibers arise, which finally terminate in the muscle walls of 

 the blood-vessels. 



THE CRANIAL NERVES. 



The cranial nerves come off from the base of the brain, pass through fora- 

 mina in the walls of the cranium, and are distributed to the structures of the 

 head, the face and in part to the organs of the thorax and abdomen. 



According to the classification of Soemmering, there are twelve pairs of 

 nerves, enumerating them from before backward, as follows viz.: 



