892 PHYSIOLOGY 



left side of the aorta and the left side of the auriculo-ventricular ring, and take an 

 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 



FIG. 392. 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 sino- 

 spiral fibres. 



to the apex, where they ako 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. 



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

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

 base. The uppermost of these fibres form circular rings round the conus arteriosus 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 heart. 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 



