530 



ANATOMY OF VERTEBRATES. 



411 



ficial layer gains in thickness as it approaches the apex, a, where 

 the course of the fibres to the inner surface of the ventricles is 

 well expressed by the term ( whorl ' or ( vortex,' fig. 411. 



Those from the fore-part of the heart, d, e,f, enter the apex 



posteriorly : those from the back 

 part of the heart, b, enter it an- 

 teriorly, at a. The curved margin 

 of the entering anterior fibres, c, 

 is left entire in successive sections 

 of the apex of the left ventricle, 

 until that of the right ventricle is 

 reached, when a more complex ar- 

 rangement appears. Most of the 

 entering fasciculi form the inner- 

 most layer of almost longitudinal 

 fibres of the ventricular cavities ; 

 others are continued into the 

 trabecular and mammillary pro- 

 cesses. 



By reflecting the superficial layer to its attachments or points 

 of inflection at the apex, <z, and at the base, b, fig. 412, the 

 second layer is exposed ; which is partly formed by fibres 



ascending from the interior 

 of the right ventricle, C acc, 

 emerging at the posterior 

 coronary tract, pet, and 

 receiving accessions from 

 the aortic and auricular 

 rings. The fibres of this 

 layer, d, take an opposite 

 course from those of the 

 first, b, c. A third layer 

 repeats the general disposi- 

 tion of the superficial one ; 

 but a larger proportion of 

 the fibres serve a single 

 ventricle, especially at the 

 apex, CRC. Many fibres 

 of this layer are derived from, or are continued into, the middle 

 layer of the septum, from which, as at fig. 413, b, the layer has 

 been cut, and reflected, at a 2, CRC, exposing the distribution 

 of the internal layers, about each ventricle exclusively, as at rv 

 and 7, fig. 413. 



Apical or vortical fibres, Human heart. 



CLXXXVII". 



412 



Mid-layers of heart fibres ; back view, clxxxviii' 



