LESSON XIII 

 THE HEART 



REGISTRATION OF THE HEART-BEAT. REFRACTORY PERIOD. EXTRA- 

 SYSTOLE. EXCISED HEART. ACTION OF STRIPS OF VENTRICULAR 

 TISSUE 



1. Normal Heart-beat. Apply a ligature to the neck of an etherized 

 turtle directly behind the occiput, and destroy the brain by pithing. 

 Saw through the lateral aspect of the ventral shield or plastron, and 

 remove the latter by cutting through the soft parts connecting it with 

 the internal structures. Keep close to the bone so as to avoid the large 

 blood-vessels. Identify the different superficial organs and note the 

 texture, extent, and mode of attachment of the pericardia! sac. Incise 

 the latter by a longitudinal cut and separate the apex of the heart by 

 dividing the strong band of connective tissue which unites it with the 

 frenum. This band should be preserved to serve later on as an attach- 

 ment for the hook of the writing lever. 



FIG. 49. ARRANGEMENT FOR REGISTERING THE CONTRACTIONS OF THE FROG'S HEART. 



(Univ. of Missouri Lab. Outlines.) 



Identify the venae cavse, sinus venosus, the right and left auricle, 

 and the ventricle with its conus and main arterial trunks (aortse). 

 Note the color and shape of the ventricle on systole and diastole, and 

 study the sequence of contraction of the different segments of the 

 heart, viz., sinus, auricles, ventricle. 



Insert a small hook in the apical band and connect it with a writing 

 lever. Counterpoise the latter sufficiently to place the ventricle under 

 a slight tension. Be sure that the plate upon which the turtle is resting 

 is placed vertically under the writing lever, so that the heart is drawn 



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