FIBRES OF THE VENTRICLES. 539 



directly backwards through the septum, forming its middle layer, to 

 the posterior ventricular groove, where it becomes joined by fibres 

 derived from the root of the pulmonary artery. It then winds spirally 

 around the middle and upper third of the left ventricle to the anterior 

 border of the septum, where it is connected by means of its internal 

 surface with the superior fibres derived from the aorta, which form 

 part of the right wall of the septum. From this point it is continued 

 around the upper third of the anterior and posterior surface of the 

 right ventricle to the posterior border of the septum, where it is con- 

 nected with the fibres constituting the right surface of the septum 

 ventriculorum. At the latter point the fibres of this band begin to be 

 twisted upon themselves, like the strands of a rope, the direction of 

 the twist being from below upwards. This arrangement of fibres is 

 called by Mr. Searle " the rope ;" it is continued spirally upwards, 

 forming the brim of the left ventricle, to the anterior surface of the 

 base of that ventricle, where the twisting of the fibres ceases. The 

 long band then curves inwards towards the septum, and spreads out 

 upon the left surface of the septum into the broad and thick layer of 

 fibres with which this description commenced. 



The most inferior of the fibres of the left surface of the septum 

 ventriculorum, after winding spirally around the internal surface of the 

 apex of the left ventricle, so as to close its extremity, form a small 

 fasciculus, which is excluded from the interior of the ventricle, and 

 expands in a radiated manner over the surface of the heart, con- 

 stituting its superficial layer of fibres. The direction of these fibres is, 

 for the most part, oblique, passing from left to right on the anterior, 

 and from right to left on the posterior surface of the heart, becoming 

 more longitudinal near its base, and terminating by being inserted into 

 the fibrous rings of the auriculo-ventricular openings, and of the pul- 

 monary artery and aorta. Over the right ventricle the superficial 

 fibres are increased in number by the addition of accessory fibres from 

 the right surface of the septum, which pierce the middle layer, and 

 take the same direction with the superficial fibres from the apex of the 

 left ventricle, and of other accessory fibres from the surface of both 

 ventricles. 



From this description it will be perceived, that the superficial layer 

 of fibres is very scanty, and is pretty equally distributed over the 

 surface of both ventricles. The middle layer of both ventricles is 

 formed by the two bands, short and long. But the internal layer of 

 the two ventricles is very differently constituted : that of the left is 

 formed by the spiral expansion of the fibres of the rope, and of the two 

 columns papillares ; that of the right remains to be described. The 

 septum ventriculorum also consists of three layers, a left layer, the 

 radiated expansion of the rope and came columns ; a middle layer, 

 the long band ; and a right layer, belonging to the proper wall of the 

 right ventricle, and continuous both in front and behind with the long 

 band, and in front also with the short band, and with the superficial 

 layer of the right ventricle. 



