FIBRES OF THE VENTRICLES. 483 



m the Cyclopaedia of Anatomy and Physiology, I am indebted for the fol- 

 lowing summary of their distribution : 



For the sake of clearness of description the fibres of the ventricles have 

 been divided into three layers, superficial, middle, and internal, all of 

 which are disposed in a spiral direction around the cavities of the ventri- 

 cles. The mode of formation of these three layers will be best understood 

 by adopting the plan pursued by Mr. Searle in tracing the course of the 

 fibres from the centre of the heart towards its periphery. 



The left surface of the septum ventriculorum is formed by a broad and 

 thick layer of fibres, which proceed backwards in a spiral direction around 

 the posterior aspect of the left ventricle, and become augmented on the 

 left side of that ventricle by other fibres derived from the bases of the two 

 columnar papillares. The broad and thick band formed by the fibres from 

 these two sources, curves around the apex and lower third of the left ven- 

 tricle to the anterior border of the septum, where it divides into two bands, 

 a short or apicial band, and a long or basial band. 



The Short or apicial band is increased in thickness at this point by re- 

 ceiving a layer of fibres (derived from the root of the aorta and carneae 

 columnae) upon its internal surface, from the right surface of the septum 

 ventriculorum ; it is then continued onwards in a spiral direction from left 

 to right, around the lower third of the anterior surface, and the middle 

 third of the posterior surface of the right ventricle to the posterior border 

 of the septum. From the latter point the short band is prolonged around 

 the posterior and outer border of the left ventricle to the anterior surface 

 of the base of that ventricle, and is inserted into the anterior border of the 

 left auriculo-ventricular ring, and the anterior part of the root of the aorta 

 and pulmonary artery. 



The Long or basial band, at the anterir border of the septum, passes 

 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 connected 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 ventri- 

 culorum, after winding spirally around the internal surface of the apex of 

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



riosus ; the letter is placed in tlie cleft formed by the bifurcation of the pulmonary r, 

 tery. g. The left pulmonary artery, h. The right ventricle, t. The point of the 

 appendix of the right auricle. 



