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HANDBOOK OF PHYSIOLOGY. 



junction of the sinus with the auricles (RemaVs); a second, -near the 

 junction between the auricles and ventricle (Bidder's)', and the third in 

 the septum between the auricles. 



It is generally believed that the rhythmical contractions of the frog's 



heart are, under ordinary circum- 

 stances, closely associated with the 

 ganglia. Thus, (1) if the heart be 

 removed entire from the body, the 

 sequence of the contraction of its sev- 

 eral beats will take place with rhyth- 

 mical regularity, viz., of the sinus 

 venosus, the auricles, the ventricle, 

 and bulbuw ^rteriosus, in order. (2) If 

 the heart be removed at the junction 

 of the sinus and auricle, the former, 

 remaining in situ, will continue to 

 beat, but the removed portion will for 

 a short variable time stop beating, and 

 when it resumes its beats, it will be 

 with a different rhythm to that of the 

 sinus; and, further, (3) if the ventricle 

 only be removed, it will take a still long- 

 er time before recommencing its pul- 

 sation after its removal than the larger "portion consisting of the auricles 

 and ventricle does in experiment (2), and its rhythm is different from 

 that of the unremoved portion, and not so regular. It will not continue 

 to pulsate so long; but during the period of stoppage a contraction will 

 occur if it be mechanically or otherwise stimulated. (4) If the lower 

 two-thirds or apex of the vetftricle be removed, the remainder of the 

 heart will go on beating regularly in the body, but the part removed will 

 remain motionless and will not beat spontaneously, although it will re- 

 spond to stimuli by a single beat for each stimulus. (5) If the heart be 

 divided lengthwise, its parts will continue to pulsate rhythmically, and 

 the auricles may be cut up into pieces, and the pieces will continue their 

 movements of rhythmical contraction. 



It will be thus seen that the rhythmical movements appear to be more 

 marked in the parts supplied by the ganglia, and that the apical portion 

 of the ventricle, in which the ganglia are not found, does not, under 

 ordinary circumstances, possess the power of automatic movement. 



It has, however, been shown by Graskell that the extreme apex of the 

 ventricle of the heart of the tortoise, which contains no ganglia, may 

 under appropriate stimuli be made to contract rhythmically. This 

 proves that the muscular tissue of the heart is capable of rhythmical 

 contraction, but it does not prove that in the living animal the muscular 



FIG. 120. Course of the nerves in the 

 auricular partition wall of the heart of a 

 frog, d, dorsal branch; v, ventral branch. 

 (Ecker.) 



