ARRAXGEMENT OF THE MUSCULAR FIBRES. 259 



passing behind the first set of fibres in the cavity, turning forwards, 

 emerges in front of them at the Jipex, around which its fibres twist, 

 to become continuous cliiefly with those superficial fibres which 

 cover the anterior surface of the heart, and are attached above to the 

 corres]")onding parts of the tendinous rings. But since the superficial 

 fil)res form a continuous stratum around the ventricles, it is impossible 

 to adjudge any exact limits to the two sets of fibres. 



It is very much more difficult to trace the continuity of the derpcr 

 fihrcs of the ventricles : those, namely, which form the main part of 

 their thickness. 



When the left ventricle is opened, the fibres forming its walls are 

 seen in the interior to take a general direction downwards, those of the 

 anterior wall converging somewhat towards the apex, those of the 

 posterior passing more diagonally from right to left. Traced upwards, 

 they are observed partly to be attached to the aortic and mitral 

 tendinous rings, partly to turn round the margin of the auriculo- 

 ventricular orifice, in continuity with other more external fibres, whicli, 

 again, come (at least some of them) from the central fibro-cartilage. 

 Traced downwards, they turn round to form the chief substance of 

 the wall of the ventricle, passing in front obliquely upwards again 

 towards the septum. Some of them, however, join the sets of fibres 

 which emerge at the apex and become superficial ; and, on the other 

 hand, the deep fibres are joined by the deeper parts of the papillary 

 muscles. Eeaching the septum, they for the most part turn into it, 

 and some of them pass at once obliquely upwards, to be attaclied to the 

 central fibro-cartilage. Others, after indenting or interlocking with 

 bundles, which turn into the septum from the front of the right ven- 

 tricle, proceed to form the posterior part of that ventricle, passing to 

 its posterior papillary muscle and the central fibro-cartilage or its prolong- 

 ations ; whilst a third set, reinforced by the entering fibres from the 

 right ventricle, take an annular course around the left ventricle. It is 

 excessively difficult to trace the ultimate destination of these anm^lar 

 bundles, for they appear to encircle the ventricle more than once, and 

 to form the main thickness of its wall : but it is probable that taking 

 a more and more oblique course, they either are eventually attached to 

 some of the tendinous or fibro-cartilaginous structures at the base, or 

 pass up into one or other of the papillary muscles at the apex. 



The bundles of fibres on the inside of the right ventricle have a 

 general direction from the tricuspid and pulmonary rings to which 

 they are attached above, and from the papillary muscles, especially 

 the anterior, towards the lower and back part of the cavity. Arrived 

 here, some turn sharply round to enter the septum, and partly to 

 pass up in this to the central fibro-cartilage, whilst others pass across 

 the back of the septum into the posterior wall of the left ventricle, 

 and become lost amongst the fibres there. There are besides certain sets 

 of fibres which appear not readily assignable to any ot those above des- 

 cribed : those, for instance, which encircle the pulmonary orifice, and others 

 which, as Sibson has shown, radiate upwards fi'om the bases of the 

 papillary muscles, especially the anterior papillary of the right ventricle, 

 to be attached to the tendinous structures at the l^ase of the heart, 

 especially to the pulmonary ring, opposite the two anterior sinuses of 

 Valsalva. Moreover, a number of fasciculi encircle both ventricles, ap- 

 parently without a definite attachment, but, according to "VVinckler, they 



