382 



TEXT-BOOK OF PHYSIOLOGY 



brachial plexus and by this route pass to the blood-vessels of the skin 

 and possibly of the muscles of the fore limb. 



The vaso-constrictors for the blood-vessels of the head, face andiieck 

 emerge from the spinal cord in the ventral roots of the first four thoracic 

 nerves. After a short course they leave the ventral roots by way of the 

 white rami and pass into the sympathetic chain after which they pass 

 upward through the ganglia and cord to the superior cervical ganglion, 

 around the cells of which these fibers arborize. From this ganglion 

 new fibers arise which follow the carotid artery and its branches to their 

 superficial terminations at least (Fig. 176$). 



Bulbarvaso-cottstrictor center 



_Btt/ltart>(r.'.ti constrictor c&iter 



.Blood vessels of head & face 



Bloodvessels of abdominal vlsc&ra 



Spinal vaso-constrictor center 



C B 



FIG. 176. Diagrams showing the course of the pre- and post-ganglionic vaso-motor fibers 

 for the blood-vessels; of A, the_ walls of the trunk of the body; of B } the head and face; and of 

 C, the abdominal viscera. 



4. The vaso-constrictors for the blood-vessels of the hind limbs emerge from 



the spinal cord in the ventral roots of the tenth thoracic to the second or 

 third lumbar nerves inclusive. They then pass by way of the white 

 rami into the corresponding ganglia around the nerve-cells of which 

 some of the fibers arborize. Others, however, descend the sympathetic 

 chain to terminate in successive ganglia as far as the third sacral ganglion. 

 From all these ganglia new nerve-fibers arise which pass backward into 

 the corresponding nerves which enter into the formation of the lumbar 

 and sacral plexuses and by this route reach the blood-vessels of the skin 

 of the lower portions of the trunk and hind limbs. 



5. The vaso-constrictors for the blood-vessels of the viscera of the abdominal 



cavity emerge from the spinal cord in the ventral roots from the fifth 

 thoracic downward. After leaving these roots by way of the white 

 rami they pass into and across the ganglia composing the thoracic por- 



