THE HEART BEATS AFTER IT IS EXCISED. 



209 



anterior aspect. The ventricle is continuous anteriorly with 

 the bulbus aortse (B), which projects in front of the right 

 auricle, and divides into two aortse right and left, the left 

 being the larger (Fig. 96). 



Fig. 97. Heart of Frog from be 

 Fig. 96. Frog's Heart from the hind. s.v, Sinus venosus opened; 



front. V, Single ventricle; Ad, 

 As, right and left auricles; B, 

 bulbus arteriosus ; 1, carotid ; 

 2, aorta; 3, pulmocutaneous ar- 

 teries ; C, carotid gland. 



c.i, inferior; c.s.d, c.s.s, right and left 

 superior vense cavse; v.p, pulmon- 

 ary vein ; Ad and As, right and 

 left auricles ; Ap, communication 

 between the right and left auricle. 



(b.) Tilt up the ventricle and observe the sinus venosus 

 (Fig. 97, s.v), continuous with the right auricle, and formed 

 by the junction of the large inferior vena cava (c.i), and the 

 two (smaller) superior vense cavse (c.s.s, c.s.d). 



3. The Heart beats after it is excised. 



(a.) With a seeker tilt up the apex of the ventricle, and 

 observe that a thin thread of connective-tissue, called the 

 " frsenum," containing a small vein, passes from the peri- 

 cardium to the posterior aspect of the ventricle. Divide it 

 with a fine pair of scissors. Count the number of beats per 

 minute. Seize with forceps the part of the frsenum attached 

 to the ventricle, and lift up the heart therewith ; and with 

 a sharp pair of scissors cut out the heart by dividing the 

 inferior vena cava, the two superior vense cavse, and the two 

 aortse. Place the excised heart in a watch-glass, and cover 

 it with another watch-glass. 



(b.) The heart goes on beating. Count the number of 

 beats per minute. Therefore its beat is automatic, and the 

 heart contains within itself the mechanism for originating 



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