XIII.] STRUCTURE AND ACTION OF THE HEART. 141 



the ventricle during its contraction or systole 

 becomes pale and conical, and that its apex 

 is thrown forwards and upwards. 



c. The slight contraction of the bulbus arteri- 

 osus immediately succeeding the ventricular 

 systole. 



d. The pause, or diastole, which follows before 

 the auricle again beats. 



e. The increased redness and distension of the 

 ventricle after the auricular, and immediately 

 preceding its own systole. 



3. Divide the band attaching the ventricle to the 

 posterior pericardial wall, and turn the apex of 

 the ventricle over. Observe 



a. The junction of the two superior venaB cava3 

 with the inferior vena cava to form the sinus 

 venosus. 



b. The white line, roughly v -shaped, marking 

 the junction of the sinus venosus with the 

 right auricle. 



c. The cardiac branches of the pneumogastric, 

 running along each superior vena cava and 

 then plunging into the interior of the 

 heart. 



d. The wave of contraction; it starts in the 

 vena cava, spreads to the sinus venosus, 



