434 



and how the fihres constituting the several external layers are con- 

 tinuous with corresponding internal layers likewise at the base*, 

 a fact to which the Lecturer drew particular attention, as being con- 

 trary to the generally received opinion, which is to the effect that the 

 fibres at the base are non-continuous, and arise from the auriculo- 

 ventricular tendinous rings which, as he showed by numerous dis- 

 sections, is not the case. 



Coming next to the question of the direction of the fibres, he 

 showed how there is a gradational sequence in the direction of the 

 fibres constituting the several layers. Thus the fibres of the first 

 layer are more vertical in direction than those of the second, the 

 second than those of the third, the third than those of the fourth, 

 and the fourth than those of the fifth, the fibres constituting which 

 layer are transverse, and run at nearly right angles to those of the 

 first layer. Passing the fifth layer, which occupies the centre of 

 the ventricular wall and forms the boundary between the external 

 and internal layers, the order of things is reversed ; and the remain- 

 ing layers, viz. six, seven, eight, and nine, gradually return to the 

 vertical in an opposite direction, and in an inverse order. This re- 

 markable change in the direction of the external and internal fibres, 

 which had in part been figured by Senac, and imperfectly described 

 by Reid f, as well as other detached and important facts ascertained 

 by himself and others such as the continuity of the fibres at the 

 apex and base, already adverted to he suggested might be accounted 

 for by the law of the double conical spiral, which he proceeded 

 forthwith to explain. 



The expression of the law, as he conceives it, with reference to 

 the arrangement of the fibres in the ventricle, is briefly the follow- 

 ing. By a simple process of involution and evolution, the external 

 fibres become internal at the apex, and external again at the base ; 

 so that whether the fibres be traced from without inwards, or from 



* The late Dr. Duncan, Jun., of Edinburgh, was aware of the fibres forming 

 loops at the hase, but seems to have had no knowledge of the continuity being 

 occasioned by the union of corresponding external and internal layers, or that 

 these basal loops were prolongations of like loops formed by similar correspond- 

 ing external and internal layers at the apex a point which the Lecturer believes 

 he is the first to establish. 



t Cyc. of Anat. and Phys., art. " Heart." London, 1839. 



