VASOMOTOR SUPPLY OF THE ORGANS. 583 



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

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

 region. The vasoconstrictors to the spleen are said to leave the 

 spinal cord chiefly in the anterior roots of the sixth, seventh, and 

 eighth thoracic nerves. 



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 

 best known of the sacral autonomic system. They enter the ner- 

 vns erigens and thence reach the organs by way of the pelvic 

 plexus. The especial importance of these fibers in the process of 

 erection is described in the section on the physiology of the repro- 

 ductive organs. The internal genital organs uterus, vagina, 

 vas deferens, seminal vesicles, etc. receive no vasomotor fibers 

 from the sacral autonomic system, that is, from the nervi erigentes 

 but do receive a supply of constrictor fibers from the sympathetic 

 system. These latter fibers emerge from the cord in the roots of 

 the upper lumbar nerves and reach the organs by way of the in- 

 ferior mesenteric ganglion and hypogastric nerve.* 



Vasomotor Supply of the Skeletal Muscles. Gaskellf es- 

 pecially has given evidence of the existence of vasomotor fibers in 

 the muscles. He concludes, as the result of his work, that the blood- 

 vessels of the muscles receive both vasoconstrictor and vasodilator 

 fibers, but that the latter greatly predominate, at least, their 

 physiological effect is much more evident in experimental work. 

 As proof of the presence of dilator fibers he gives such results as 

 these: The mylohyoid muscle of the frog is thin enough to be 

 observed directly under the microscope. When curarized and 

 stimulated through its motor nerve the small vessels may be seen 

 to dilate and there is an augmented flow of blood. In a dog section 

 of the motor nerve to a muscle is followed by a greatly increased 

 flow of blood, which, however, is only temporary and is referable to 

 a mechanical stimulation of the dilator fibers. Direct stimulation 

 of the severed nerve causes an increased flow of blood through the 

 muscles, but if the muscles are first completely curarized stimulation 

 causes, on the contrary, a decreased flow. This last result is ex- 

 plained on the supposition that curare paralyzes the endings of the 



* For the bibliography of the vasomotor supply to the various organs see 

 Langley, "Ergebnisse der Physiologic," vol. ii., part n., p. 820, 1903. 

 tGaskell, ' Journal of Physiology," 1, 262, 1878-79. 



