THE MECHANISM OF THE HEART PUMP 1005 



the left ventricle. The middle layer is connected by many strands of 

 muscular fibres with both inner and outer layers. 



Mall divides the muscular fibres of the mammalian heart into four groups, 

 two superficial and two deep, as follows : 



(1) The superficial bulbo-spiral fibres. These arise from the conus arteriosus, 

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



FIG. 388. 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. 



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 intra- 

 ventricular 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. 



(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. 



