VASODILATOR NERVES 233 



The tail gets its vasoconstrictor nerves from the third to the fourth lumbar 

 nerves; and the dorsal side of the trunk from the posterior branches of the spinal 

 nerves corresponding to the different segments of the back. 



The nerves pass from their origin through the trunk of the sympathetic 

 and from there for the most part to the different organs of the body by way 

 of the chief nerve trunks. 



The vasoconstrictor nerves of the abdominal viscera leave the spinal cord 

 by the third thoracic to the first or third lumbar nerves, run for the most part 

 in the splanchnics, and are distributed by them to the different organs of the 

 abdominal cavity. The nerves of the large intestine pass out of the spinal cord 

 in the seventh thoracic to the second lumbar nerves; those of the liver in the 

 sixth thoracic to the second lumbar; those of the pancreas in the fifth thoracic 

 to the first lumbar nerve. 



The vasoconstrictor nerves of the organs of generation pass out in the last 

 lumbar and in the first sacral nerves, and proceed to their end arborizations 

 through the hypogastric plexus. 



The lungs also possess vasoconstrictor nerves; according to the majority of 

 authors, they leave the spinal cord in the second to the fifth thoracic nerves, and 

 proceed by way of the sympathetic paths to the lungs. Recently the presence 

 of vasomotor nerves in the lungs has been absolutely denied. 



Vasoconstrictor nerves appear to traverse other paths also. Thus we find 

 in the second and third nerves of the cervical plexus vasoconstrictor fibers for 

 the tip and lateral parts of the ear, which reach their destination by way of the 

 auricularis cervicalis nerve. It is further asserted that the vagus conveys vaso- 

 constrictor nerves to the heart, to the stomach, to the intestine (not confirmed 

 by all authors) and to the kidneys, and also that in it are contained vasocon- 

 strictor fibers for the lungs. It is indeed not impossible that these fibers might 

 arise from the sympathetic (since it is definitely asserted that the vasoconstrictor 

 nerves in the auricularis cervicalis arise in the thoracic sympathetic and run 

 through the stellate ganglion), and it is also conceivable that they actually 

 belong to the branches of the vagus. 



Because of the great vascular territory committed to their control the 

 splanchnics play the most important part of all vasomotor nerves. For this 

 reason the blood pressure falls after bilateral section of these nerves, and 

 shows a very great rise on stimulation of them. 



Constricting nerve fibers have been demonstrated also for the veins. If the 

 aorta be tied off immediately below the origin of the left subclavian, and the 

 blood supply to the hinder part of the body be thereby cut off, stimulation of 

 the splanchnics drives through the inferior vena cava into the right heart a 

 quantity of blood which runs up to twenty-seven per cent of the total quantity 

 in the animal. According to Mall, this is caused by contraction of the portal 

 system. 



Constrictor effects of nerve stimulation in other veins are mentioned by dif- 

 ferent authors ; but R. F. Fuchs has published experiments in which he obtained 

 no active constriction of the veins either by direct stimulation of the veins them- 

 selves or by electrical stimulation of nerves, wherefore he denies entirely the 

 presence of vasomotor nerves for the veins. 



Finally, the musculature of the vessels contracts under high internal pres- 



