UPON THE VASCULAR SYSTEM. 109 



The heart is connected with the vagus by a superior and an inferior branch. 

 The former, in the rabbit, leaves the vagus with the superior laryngeal nerve, 

 or it may be somewhat below the origin of the latter ; it courses down the back 

 in close proximity to the sympathetic, joins one or two branches of the inferior 

 cervical ganglion with which it proceeds to the heart. In dogs this nerve is 

 bound up with the trunk of the vagus and cervical sympathetic in one common 

 trunk ; in cats it is joined to the sympathetic. The function of this nerve 

 was discovered by Ludwig and Cyon.* It is a vaso-inhibitory and also an 

 excitocardio-inhibitory nerve ; that is to say, when it acts it dilates vessels, 

 and it also excites the filaments of the vagus (inferior cardiac branch) which 

 inhibit the heart's movements. The influences which travel through the nerve 

 start from the heart and pass to the medulla oblongata, there to inhibit the 

 nerve-cells in the medulla connected with the motor nerves for the abdominal 

 blood-vessels, and also to excite the nerve-cells in the medulla connected 

 with the cardio-inhibitory fibres of the vagus. This nerve was named by 

 the discoverers of its function " Nervus Depressor," because it lowers the 

 blood-pressure ; this it does by diminishing the work done by two great portions 

 of the vascular system — the heart — and abdominal blood-vessels. The in- 

 fluences which travel through the nerve pass towards the medulla, probably 

 their only starting-point is in the heart ; but with the cause which determines 

 the action of the nerve we are totally unacquainted. Its discoverers always 

 failed to find it in action ; that is to say, they never saw the blood-pressure 

 rise when the nerve was divided. This of course was a very unsatisfactory 

 circumstance, not a little calculated to cast grave doubts as to the real function 

 of the nerve having been discovered at all. I am glad to say, however, that in 

 the course of experiments hereafter to be detailed, I succeeded in finding this 

 nerve in action on several occasions (see Experiments XLL, XLIV., XL VI., 

 LI.) The nerve certainly acts in the manner indicated by Ludwig and Cyon ; 

 but my experiments do not enable me to state what are the causes of its being 

 thrown into action. 



The inferior cardiac branch of the vagus usually arises with the inferior 

 laryngeal nerve, and from this origin it proceeds to the heart, where, according 

 to BEALE,t it joins the cells of the cardiac ganglia.;): 



* Sachs. Acad. Bericht, 1866, p. 307. 



f Philosoph. Trans. 1863, p. 562, and fig. 41. 



X From physiological evidence it is generally believed that the cardio-motor nerves (sympathetic) 

 are also connected with the ganglia in the heart. The termination of the depressor nerves ■within the 

 heart is quite unknown. 



