THE HEART 67 



kept in this cistern by valves, e.g. femoral and jugular, and the 

 pressure caused by the body movements must therefore send the 

 blood on to the right heart. 



The chief function of the right auricle, however, is to expel the 

 blood into the right ventricle at the end of joint diastole, and 

 thereby place its walls on a certain tension. According to this 

 degree of tension the heart muscle will contract. Within certain 

 limits, the greater the tension, the more powerful the contraction. 

 It is by this means in part, that the amount of blood passing to 

 and from the heart is regulated to meet the needs of the body in 

 general. 



It is necessary, therefore, to inquire into the movements acc:m- 

 panying auricular systole. The key to them lies in the study of 

 the auricular and ventricular musculature. The function of the 

 musculi pectinati of the auricle has been neglected. In the human 

 heart they are fifteen to eighteen in number, and from 1 to 2 mm. in 

 diameter. They take origin from the right tsenia terminalis, and 

 end in the musculature of the auricular canal in the A-V groove. 

 The tamia terminalis is a fixed point through the venous meso- 

 cardium ; therefore when the musculi pectinati contract, they are 

 drawn towards the fulcrum, the ventricle being also drawn up at 

 the same time. It will therefore be seen that this movement 

 which empties the auricle at the same time draws the ventricle 

 over its load. There is therefore in auricular systole a movement 

 of the A-V groove towards the venous base of the heart. This 

 function of the musculi pectinati has been well demonstrated by 

 injecting warm wax into the auricle, the casts so obtained showing 

 that the musculi pectinati shorten to quite half their diastolic 

 length during systole (Keith). In hearts from cases of back pres- 

 sure there is great prolongation and hypertrophy of these muscles. 

 Now an anatomical axiom is that every muscle in the body has 

 its opponent, the opponent in this case being part of the inner 

 longitudinal layer of muscle of the right ventricle. Inspection of 

 the ventricle will show two layers of muscle an inner longitudinal 

 and an outer spiral layer. The longitudinal layer can bs divided 

 into two systems (1) That to the auricle or venous base ; (2) that 

 to the aortic exit or arterial base. The significance of the system 

 to the arterial base is perhaps at first not quite apparent. Accord- 

 ing to Keith, its function is to act with the spiral fibres in 

 rendering the apex a fixed point. The spiral fibres will tend by 



