THE HEART. 329 



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 dis- 

 tinctly marked ; and that these layers, as was exhibited in various dis- 

 sections, 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,* 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 certain 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 inter- 

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

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

 the fifth or central one, which is transverse, is reached, they cross at 

 successively wider vertical angles, as may be represented by an M 

 placed horizontally. 



" Holding the cone, prepared as described, against the light, the Lec- 

 turer then showed how, by the rolling process, a double system of 

 conical spirals, similar to those found in the left ventricle, had been 

 produced the one an external left-handed down system, running from 

 base to apex, and corresponding with the external layers ; the other an 

 internal right-handed up system, running from apex to base, and 

 corresponding with the internal fibres ; and how, seeing the opposite 

 systems are the result of different portions of the same threads being 

 rolled in different directions (the one within the other), the spirals are 

 consequently continuous at the apex. 



mends. The sheets should be twice as long as they are broad; and the 

 lines or threads should run in the direction of the length. 



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



