328 THE HEART. 



clinous rings, which, as he showed by numerous dissections, 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 remaining 

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

 in an opposite direction, and in an inverse order. This remarkable 

 change in the direction of the external and internal fibres, which had 

 in part been figured by Senac, and imperfectly described by Reid,* 

 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 following. 

 By a simple process of mvolution and evolution, the external fibres be- 

 come internal at the apex, and external again at the base ; so that 

 whether the fibres be traced from without inwards, or from within out- 

 wards, they always return to points not wide apart from those from 

 whence they started. In order to illustrate the principle of the double 

 conical spiral in the above sense, he took a sheet of net, through which 

 parallel threads of coloured wool, representing the individual fibres, 

 were drawn at intervals ; and laying it out on the table before him, 

 with the threads placed horizontally, seized it by the right-hand off 

 corner, and rolled it in upon itself (i. e. towards his own body) seven 

 turns, so as to produce a cone whose walls consisted of nine layers.t 



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



f A sheet of paper with parallel lines drawn upon it will answer the pur- 

 pose equally well, except that its non- transparency precludes our seeing the 

 external and internal spirals rolled the one within the other when the sheet 

 is fashioned into a cone and held against the light, as the Lecturer recom- 



