FIBRES OF THE VENTRICLES. 639 



less and less oblique, until, at last, they are nearly transverse, ex- 

 cepting such as ascend on the inside of the ventricles. According to 

 their mode of dissection, different anatomists make different numbers 

 of layers, and some divide these into numerous component bands. Ac- 

 cording to Pettigrew, the latest authority, there are seven layers, three 

 outer ones, the fibres of which become successively less and less oblique 

 downwards from right to left, a central transverse layer, and three 

 inner ones, the fibres of which become more and more oblique in the 

 opposite direction. 



The ventricular fibres, whether superficial or deep, have long been 

 known to form spirals, at and near the apex of the heart, the super- 

 ficial fibres forming a completely closed spiral, and each succeeding 

 layer a more open one. Hence, on looking directly at the apex of 

 the heart, a remarkable whorl, or vortex, of fibres is seen, in which 

 these appear, in turn, to sink towards the interior of the ventricles ; 

 if the fibres of each layer be now raised up and removed, the vortex 

 becomes more and more open, and at length the cavities of the ven- 

 tricles are exposed. 



It was believed by Lower, Gerdy, Reid, and other anatomists, that 

 the ventricular fibres chiefly, if not entirely, arise from the auriculo- 

 ventricular fibrous rings, and that, after passing spirally round the 

 heart, they turn upon themselves at the apex, there forming, as indi- 

 cated especially by Lower and Gerdy, twisted continuous loops, and 

 then pass up directly through the walls or septum of the ventricles, 

 back to the fibrous rings again, or reach them indirectly, through the 

 musculi papillares and chordae tendinese of the tricuspid and bicuspid 

 valves. In short, the fibres of the ventricles were described as forming 

 loops, open towards the base of the heart, but closed, and twisted into 

 a vortex, at the apex. However, according to Duncan, the fibres form 

 loops in the direction of the base, as well as in that of the apex ; 

 and Pettigrew affirms that none, or almost none, are attached to the 

 fibrous rings, but pass by them, in the form of loops. Moreover, the 

 elaborate dissections of the last-named anatomist show, that just as, 

 at the apex, the superficial fibres penetrate, to become, as has been 

 long known, the deep-seated fibres, so, at the base, the superficial fibres 

 are likewise continuous with the deepest fibres. 



In the left ventricle, which Pettigrew regards as the typical ven- 

 tricle, the first, or superficial layer, passes, both at the apex and base, 

 into the innermost or seventh layer, the second into the sixth, and the 

 third into the fifth ; the fourth layer is central, and forms a transverse 

 layer situated between the third and fifth. Each successive double layer 

 incloses the next in order, and the necessary limitation of the central 

 layer, and its absence at the apex and base, account for the greater 

 thickness of the walls of the left ventricle, across its middle. The 

 spiral fibres, which may be traced from the front of the auriculo-ven- 

 tricular opening, pass over the anterior surface of the ventricle, and, 

 after describing one turn and a half, dip into the apex posteriorly ; 

 whilst those coming from the back of that opening, pass over the 

 hinder surface of the ventricle, wind forward, and enter the apex an- 

 teriorly ; after dipping inwards, the former end in the anterior musculi 



