THE CIRCULATION OF THE BLOOD. 369 



The following facts will serve as illustrations of the functions of vaso- 

 constrictor nerves. Division of the great splanchnic is followed by a marked 

 dilatation of the blood-vessels of the intestinal tract and a decided fall in 

 blood-pressure; stimulation of the peripheral end by their contraction and a 

 marked rise in blood-pressure. Division of the cervical cord of the sym- 

 pathetic is followed by dilatation of the blood-vessels of the side of the head; 

 stimulation of the peripheral end by their contraction. 



The Vaso-dilatator Nerves. The vaso-dilatator nerves have their 

 origin for the most part as generally believed in nerve-cells situated in 

 the region of the spinal cord included between the origins of the second 

 dorsal to the second lumbar nerves inclusive, though they are not confined 

 to this region. Some vaso-dilatator fibers have their origin in the medulla 

 oblongata, others in the sacral region of the spinal cord. 



Vaso-dilatator fibers have been found in association with vaso-constrictor 

 fibers in most of the nerve trunks of the body though they are perhaps not 

 so abundant. Thus the results of experimentation indicate that they are 

 present in the cervical portion of the sympathetic in the nerve trunks of 

 the upper and lower limbs, in the nerve trunks of the body walls, and in the 

 splanchnics. The exact path, however, through which they pass from the 

 spinal cord to the peripheral nerve trunks has not in all cases been positively 

 determined. The cell stations also in which the pre-ganglionic fibers 

 terminate have not in all cases been located. There are reasons for the 

 opinion, however, that they follow somewhat the same paths as the vaso- 

 constrictor fibers. 



The vaso-dilatator fibers that arise in the medulla oblongata pass out in 

 the trunk of the pars intermedia or nerve of Wrisberg and in the trunk of 

 the glosso-pharyngeal nerve. Those fibers which are contained in the nerve 

 of Wrisberg, enter, after a short course, the trunk of the facial nerve and 

 through its branches the great petrosal and the chorda tympani, are ulti- 

 mately distributed as pre-ganglionic fibers to the spheno-palatine and sub- 

 maxillary and sublingual ganglia respectively. From the spheno-palatine 

 ganglion cells post-ganglionic fibers are distributed to the blood-vessels of the 

 mucous membrane of the nasal chambers posteriorly, and to adjacent regions. 

 From the submaxillary and sublingual ganglia post-ganglionic fibers pass to 

 the blood-vessels of the submaxillary and sublingual glands. 



The vaso-dilatator fibers that are contained in the glosso-pharyngeal 

 nerve pass through the tympanic plexus by way of Jacobson's nerve to the 

 otic ganglion, around the cells of which their end branches arborize; from 

 the cells of this ganglion post-ganglionic fibers pass to the walls of the 

 blood-vessels of the parotid gland and of the cheek and gums. 



The vaso-dilatators that emerge from the sacral region of the spinal 

 cord, pass by way of the second and third sacral nerves as preganglionic 

 fibers to ganglia situated near the blood-vessels supplying in both sexes, 

 the organs of generation and adjacent structures. From the ganglia post- 

 ganglionic fibers are distributed to the walls of these blood-vessels. 



The existence, course, distribution, and functions of the vaso-dilatator 

 fibers have been determined by the same methods employed as in the investi- 

 gation of the vaso-constrictors. Thus division and appropriate stimulation 

 of the peripheral end of the cervical sympathetic will be followed by a con- 

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