THE HEART. 



277 



toward the apex, curling round the heart in such a manner as to 

 pass over its anterior surface in an obliquely spiral direction, from 

 above downward, and from right to left. (Fig. 88.) They converge 



toward the point of the heart, curl- 

 ing round the centre of its apex, and 

 then, changing their direction, be- 

 come deep-seated, run upward along 



Fig. 89. 



BULLOCK'S HK AKT, anterior view, 

 showing thesupe.ficial muscular fibres. 



T- E F T V E x T R r r r. E OF 

 Bp i. LOCK'S HEAKT, show- 

 iug the deep fibres. 



the septum and internal surface of the ventricles, and terminate 

 in the columns earner, and in the inner border of the auriculo- 

 ventricular ring. The deepest layers of fibres, on the contrary, a*re 

 wrapped round the ventricles in a nearly circular direction (Fig. 

 89) ; their points of origin and attachment being still the auriculo- 

 ventricular ring, and the points of the fleshy columns. The entire 

 arrangement of the muscular bundles may be readily seen in a 

 heart which has been boiled for six or eight hours, so as to soften 

 the connecting areolar tissue, and enable the fibrous layers to be 

 easily separated from each other. 



By far the greater part of the mass of the fibres have therefore 

 a circular instead of a longitudinal direction. When they contract, 

 their action tends to draw the lateral walls of the ventricles together, 

 and thus to diminish the transverse diameter of the heart; but as 

 each muscular fibre becomes thickened in direct proportion to its 

 contraction, their combined lateral swelling necessarily pushes out 

 the apex of the ventricle, and the heart elongates at the same time 

 that its sides are drawn together. This effect is illustrated in the 

 accompanying diagram (Fig. 90), where the white lines show the 

 figure of the heart during relaxation, with the course of its circular 



