562 CIRCULATION OF BLOOD AND LYMPH. 



The Trunk and the Limbs. The vasoconstrictor fibers for 

 these regions are distributed, so far as is known, chiefly to the skin. 

 They are all derived immediately from the sympathetic chain and 

 ultimately from the outflow in the anterior roots of the thoracic 

 and lumbar spinal nerves. Those for the upper limbs arise from 

 the midthoracic region chiefly (fourth to ninth thoracic nerves), 

 those for the lower limbs arise in the nerves of the lower thoracic 

 and upper lumbar region (eleventh, twelfth, thirteenth thoracic 

 [dog] and first and second lumbar). The vasodilator fibers in the 

 nerves of the limbs have been demonstrated frequently, as already 

 explained. Whether or not such fibers are found in the sympathetic 

 system following the same general course as the constrictors has 

 not been shown conclusively. The most definite work at present 

 (Bayliss) indicates that the vasomotor effect is directly caused in 

 some unknown way by sensory fibers arising in the posterior roots 

 of the nerves forming the brachial and the sciatic plexus. The 

 unsatisfactory explanations offered for this result have been re- 

 ferred to (p. 548). 



The Abdominal Organs. The stomach and intestines receive 

 their most important supply of vasoconstrictor fibers by way of the 

 splanchnic nerves and celiac ganglion. These fibers emerge from 

 the cord in the lower thoracic spinal nerves, from the fifth down, 

 and the upper lumbar nerves, and they supply the whole mesenteric 

 circulation as far as the descending colon. According to some 

 observers (Francois-Franck and Hallion), the mesenteric vessels 

 receive a supply of vasodilator fibers by the same general route, and 

 it is also stated that similar fibers reach this region through the vagus 

 nerve. Concerning this latter statement at least further con- 

 firmation is necessary. The pancreas has been shown to receive 

 vasoconstrictor fibers by way of the splanchnics, and the kidney, 

 according to Bradford, receives vasodilator as well as vasocon- 

 strictor fibers from the same nerve. Most of the vasomotor fibers to 

 the kidney of the dog emerge from the cord in the roots of the 

 eleventh, twelfth, and thirteenth thoracic nerves, and those for the 

 liver (Frangois-Franck and Hallion) come from about the same 

 region. The vasomotor supplies of the spleen and the bladder have 

 not as yet been investigated successfully. 



The Genital Organs. Both vasoconstrictor and vasodilator 

 fibers have been discovered for the external genital organs (penis, 

 scrotum, clitoris, vulva). The vasoconstrictors arise in the dog 

 from the thirteenth thoracic to the fourth lumbar nerves, pass over 

 to the sympathetic chain, and thence reach the organs either by 

 way of the hypogastric nerve and pelvic plexus or by way of the 

 sacral sympathetic ganglia and their branches to the pudic nerves. 

 The vasodilator fibers arise from the sacral spinal nerve, being the 



