CARDIAC NERVES 



73 



Be careful not to injure the heart more than is absolutely necessary. 

 Jn order to fix the base securely, pass a strong pin close to the base 

 of the heart and through the vertebral column into the frog-cork. 



The following experiments may be performed upon this prepara- 

 tion : 



1. Take a normal tracing of the beats during a short period and 

 record by an electromagnetic signal a time-tracing (seconds) upon the 



Glossopharyngeal. . -/- -> 



Vagus. 



Laryngeal branch of vagus. 

 Hypoglossal. - 



2nd spinal (or brachial) nerve. _ -Nv^ 



Cardiac branch of vagus. 



Superior vena cava. 



i'ulrnoiiary branches of vagus. -V 



Glottis. 



Left auricle. 

 Bulbus aortee. 

 ^ Right auricle. 



Sinus venosua. 



FIG. 62. RELATIONS OF VAGUS NERVE TO OTHER STRUCTURES IN THE NECK AND THORAX. THE 

 VENTRIOI^E HAS BEEN DRAWN OVER TO THE LEFT SIDE BY A HOOK AND THE SINUS VENOSUS is 

 THUS EXPOSED, x , LINE OF JUNCTION BETWEEN SINUS AND AURICLES. 



drum. This time-tracing is to serve for determining the exact rate 

 of the heart-beat under the different circumstances of the experiments. 



2. Whilst this is proceeding, stimulate, not too strongly, the 

 medulla oblongata, allowing the result to be recorded continuously 

 at the same level of the drum. 



3. Cut both vagus nerves near the skull and repeat the above 

 stimulation of the medulla oblongata, recording the result at another 

 level of the drum. 



4. Alter the commutator and stimulate the vagus, recording the 

 result at a third level of the drum. With weak stimulation of the 

 vagus in the frog the heart may beat faster and more strongly owing 



