422 THE NERVOUS REGULATION OF THE BLOOD-VESSELS 



entiating between the nervous effects and those caused by the contract- 

 ing muscle fibers. GaskelP states that the excitation of the distal end 

 of the motor nerve of the mylohyoid muscle gives rise to a dilatation 

 which persists even after the administration of curare. Besides, the 

 determinations of the blood supply of the gracilis muscle of dogs, 

 which have been undertaken by Burton-Opitz^ and Tschuewsky,^ 

 have shown that the flow is greatly diminished during the period of 

 contraction of the muscle but much increased during its relaxation. 

 It need scarcely be emphasized that these changes may be chiefly 

 mechanical and must occur whenever the motor nerve of a muscle is 

 stimulated. This is shown by the fact that the tetanization of the 

 muscle reduces the blood flow almost to zero. We have no means of 

 differentiating between these mechanical effects and those of vasomotor 

 origin,: unless we should paralyze the motor plates by means of curare. 

 But again, inasmuch as this agent might also affect the vasomotor ter- 

 minals in muscle, it could not serve as a means to decide this question 

 one way or another. This uncertainty regarding the existence of 

 vasomotor nerves in muscle tissue, has not been lessened by the experi- 

 ments of Kaufmann,* who has ascertained that the blood flow through 

 the masseter muscle of the horse may be increased as much as five times 

 by permitting this animal to masticate normally. Instead of referring 

 this change to a stimulation of the nervous mechanism, we might 

 attribute it with equal justification to a mechanical widening of the 

 blood-vessels. This explanation might be adhered to in spite of the 

 fact that this action is associated with a fall in pressure in the artery 

 supplying this muscle, and an increase in pressure in the vein draining 

 it. 



The Trigeminus Nerve. — This nerve embraces vasoconstrictor 

 fibers for the conjunctiva, the sclerotic coat and iris of the eye, as 

 well as for the mucous lining of the nose and gums. Its lingual branch 

 innervates the blood-vessels of the tongue. In the rabbit, the auricu- 

 laris magnus nerve, a branch of the third cervical, embraces vaso- 

 motor fibers for the ear. 



The Cervical Sympathetic Nerve. — This nerve forms the connec- 

 tion between the inferior and superior cervical ganglia. During its 

 course along the neck, it lies in relation with the carotid artery and 

 the vagus nerve. In some animals, such as the rabbit, it pursues an 

 independent course, while in others it attaches itself to the vagal fibers 

 (cat) or becomes completely intermingled with them (dog). Distally 

 to the superior cervical ganglion, the individual fibers follow in the 

 path of the blood-vessels and finally attain such structures as the 

 cerebrum, the ear, submaxillary gland, larynx, thyroid body, and 

 the integument of the head. 



1 Jour, of Physiol., i, 1878, 108. 



2 Am. Jour, of Physiol., ix, 1902, 161. 



3 pfliiger's Archiv, xcvii, 1903, 289! 



4 Arch, de Physiol, et Path., 1892. 



