PHYSIOLOGY OF THE CIRCULATION. 



LESSON XLIV. 



THE FROG'S HEART BEATING OF THE 



HEART EFFECT OF HEAT AND GOLD 



SECTION OF THE HEART. 



1. The Heart of the Frog and how to expose it. 



(a.) Pith a frog, and lay it on its back on a frog-plate. 

 Make a median incision through the skin over the sternum, 

 and from the middle of this make transverse incisions. 



(b.) Reflect the four flaps of skin, raise the lower end of 

 the sternum with a pair of forceps, and cut through the 

 sternal cartilage just above its lower end to avoid wounding 

 the epigastric vein. With a strong pair of scissors cut along 

 the margins of the sternum, and divide it above transversely 

 to remove the anterior wall of the thorax. This exposes 

 the heart, still enclosed within its pericardium, where it can 

 be seen beating. 



(c.) With a fine pair of forceps carefully lift up the thin 

 transparent pericardium, cut it open, thus exposing the 

 heart. 



2. Study the General Arrangement of the Frog's Heart. 



(a.) Observe its shape, noting the two auricles above 

 (Ad, As), and the conical apex of the single ventricle 

 below (v), the auricles being mapped off from the ventricle 

 by a groove -or furrow which runs obliquely across its 



