435 



within outwards, 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 con- 

 sisted of nine layers*. On gradually unwinding the walls of the 

 cone thus fashioned (which is tantamount to undoing the spirals), so 

 as to imitate the removal of consecutive layers from the walls of the 

 ventricle, he finds that the gradation in the direction of the several 

 layers just specified is distinctly marked ; and that these layers, as 

 was exhibited in various dissections, find a counterpart in the ventricle 

 itself. Thus (the heart being supposed to be placed upright on its 

 apex) in the first external layer the threads are seen running from 

 base to apex, and from left to right f, almost vertically; in the 

 second layer they are slightly oblique ; this obliquity increases in 

 the third, and still more in the succeeding layer, till in the fifth or 

 central one the direction of the threads becomes transverse. After 

 passing the central layer, the direction of the threads (as of the 

 fibres) is reversed ; in the sixth layer they begin to turn from right 

 to left, with a slight inclination upwards ; and in succeeding layers 

 gradually become more and more vertical, until the innermost, or 

 ninth, is reached, in which they -become as vertical as in the first, 

 but are curved in an opposite direction. 



As a necessary consequence of this arrangement of the fibres, the 

 Lecturer showed that when the layers are in apposition, as they 

 exist in the undissected ventricle, the first external layer and the last 

 internal cross each other with a slight deviation from the vertical, as 

 in the letter X ; while in the succeeding external and internal layers, 



* A sheet of paper with parallel lines drawn upon it will answer the purpose 

 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 recommends. The sheets 

 should be twice as long as they are broad j and the lines or threads should run in 

 the direction of the length. 



t That is, in the direction from the left hand to the right of the observer. 



