484 STRUCTURE OF THE HEART. 



which is excluded from the interior of the ventricle, and expands in a 

 radiated manner over the surface of the heart, constituting 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 pos- 

 terior surface of the heart, becoming more longitudinal near its base, and 

 terminating oy being inserted into the fibrous rings of the auriculo-ventri 

 cular openings, and of the pulmonary artery and aorta. Over the righ 

 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 sur- 

 face 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 columnar 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 carnese 

 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. 



The Internal layer of the right ventricle is formed by fasciculi of fibres 

 which arise from the right segment of the root of the aorta, from the entire 

 circumference of the root of the pulmonary artery, and from the bases of 

 the columnar papillares. The fibres from the root of the aorta, associated 

 with some from the carnea? columnar, constitute a layer which passes ob- 

 liquely forwards upon the right side of the septum. The superior fibres 

 coming directly from the aorta join the internal surface of the long band 

 at the anterior border ,of the septum, w r hile the lower two-thirds of the 

 layer are continuous with the internal surface of the short band, some of 

 its fibres piercing that band to augment the number of superficial fibres. 

 The fibres derived from the root of the pulmonary artery, conjoined with 

 those from the base of one of the columnar papillares, curve forwards from 

 their origin, and wind obliquely downwards and backwards around the 

 internal surface of the wall of the ventricle to the posterior border of the 

 septum, where they become continuous with the long band, directly that 

 it has passed backwards through the septum. 



Fibres of the Jluricles. The fibres of the auricles are disposed in two 

 layers, external and internal. The internal layer is formed of fasciculi 

 which arise from the fibrous rings of the auriculo-ventricular openings and 

 proceed upwards to enlace with each other, and constitute the appendices 

 auricularum. These fasciculi are parallel in their arrangement, and in the 

 appendices form projections and give rise to the appearance which is de- 

 nominated musculi pectinati. In their course they give ofT branches which 

 connect adjoining fasciculi, and form a columnar interlacement between 

 them. 



External Layer. The fibres of the right auricle having completed the 

 appendix, wind from left to right around the right border of this auricle, 

 and along its anterior aspect, beneath the appendix, to the anterior surface 



