LABORATORY MANUAL OF PHYSIOLOGY. 



How do the contraction curves compare with each other ? 



How does the time ocupied by the systolic phase compare with 

 the time occupied by the diastolic phase in each tracing ? 



When the frequency of the heart-beat is increased, is the time 

 occupied by systole and that of diastole decreased in the same 

 ratio ? 



If not, which is shortened the more, systole or diastole ? 



V. DISSECTION OF THE EXTRINSIC CARDIAC NERVES or THE 



FROG. 



With a preserved or fresh dead frog, expose the heart as before. 

 Carefully cut away the sternum and muscles of the thorax. Locate 

 the glosso-pharyngeal and hypoglossal nerves (see Fig. 28). Also 



H 



FIG. 28. Extrinsic Cardiac Nerves of Frog. V, Vago-sympathetic ; Gp, glosso- 

 pharyngeal nerve ; Hg, hypoglossal nerve ; Br, brachial plexus ; /., laryngeal nerve ; 

 //, heart ; Lv, lung. 



note the petrohyoid muscle. Along the lower border of this muscle 

 and lying between the loops of the above-mentioned nerves, are 

 two fine grayish fibres. These are, the lower one the vagus trunk, 



[86]. 



