936 



PHYSIOLOGY 



oblique course to the apex, where they make a spiral turn (the vortex) and reach the 

 interior of the left ventricle, ending for the most part in the intraventricular septum 

 and the papillary muscles. 



(2) The superficial sino-spiral fibres rise on the dorsal side of the heart from the right 

 auriculo-ventricular ring and run obliquely on the anterior surface of the right ventricle 

 to the apex, where they also turn inwards, forming the anterior horn of the ' vortex,' 

 and end chiefly in the papillary muscles of the right ventricle. 



(3) The deep bulbo-spiral fibres form a complete cylinder around the left ventricle, 

 and are attached chiefly to the dorsal side of the aorta. 



FIG. 402. View of the heart from behind, to show the course of the chief 

 strands of muscle fibres. (MALL.) 



The black lines represent the bulbo-spiral fibres, the grey lines the swo- 

 spiral fibres. 



(4) The deep sino-spiral fibres are attached to the dorsal aspect of the left aurieulo- 

 ventricular ring, wheiiee they enter the right ventricle and turn upwards towards the 

 base. The uppermost of these fibres form circular rings round the con UN url< rioxii* at 

 the base of the pulmonary artery. 



The fact that the muscular fibres are continuous over both auricles and 

 over both ventricles respectively ensures the practically simultaneous con- 

 traction of each of these parts of the hea.rt. Although on coarse dissection 

 there seems to be absolute division between the muscular tissue of auricles 

 and ventricles, it has been shown by Kent, His, and others that there is 

 continuity of muscular tissue between the two parts of the heart by a special 

 band of muscular fibres, 'the bundle of His." which rises in the wall of the 

 ii:ht auricle and passes beneath the for amen <>/<//<' and across the auriculo- 



