99° 



A MANUAL OF ANATOMY 



others pass across to the postero -inferior wall of the right ventricle, where 

 they partly end in a musculus papillaris, and partly pass to be attached to 

 the right auriculo -ventricular fibrous ring; whilst a third set pass to the 

 postero-inferior wall of the left ventricle, where they become circular in 

 direction. The principal fasciculi of the right ventricle are, like the super- 

 ficial fasciculi, continuous with those of the left ventricle, and they spring 

 from the fibrous rings around the auriculo-ventricular and pulmonary orifices. 

 Those on the postero-inferior surface of the right ventricle pass into the 

 interventricular septum, and, having traversed it obliquely forwards and 

 upwards, they issue from it, and become continuous with the deep fibres of 

 the left ventricle. Those on the antero-superior surface of the right ventricle 

 also pass into the interventricular septum, and having traversed it obliquely 

 backwards and downwards, they pass on to the postero-inferior wall of the 

 left ventricle. Those from the inferior aspect of the right ventricle enter the 

 lower part of the interventricular septum, and ascend in the septum to the 

 collection of dense fibrous tissue of the consistence of fibro-cartilage at the 

 base. Although the ventricular muscular fasciculi are disposed for the most 

 part obliquely, there are some circular fasciculi, but these are confined to the 

 thickest part of each ventricular wall. 



Fibres of Purkinje. — These fibres are situated between the endocardium 

 and the cardiac muscular tissue. They consist of elongated cells, united at 

 their ends so as to form chains. The central part of each cell contains granular 

 protoplasm, within which there are two nuclei; and the peripheral part 

 presents transverse striations. These cells are probably vestiges of an early 

 condition of cardiac muscular fibres. 



Fig. 408.- 



-The Superficial Muscular Fibres of the Heart in the 

 Region of the Apex (C. Gegenbaur). 



The whorled arrangement is well shown. 



Auriculo-Ventricular Bundle. — This bundle constitutes the only auriculo- 

 ventricular muscular connection, and functionally it is of a conducting nature. 

 It may be described in three sections — auricular (atrial), nodal, and ventricular. 



The auricular section consists of fibres which are derived from (i) the 

 circular fibres of the right auricle, just above the base of the septal cusp 

 of the tricuspid valve, and (2) the muscular tissue of the interauricular 

 septum at a point situated at the lower and anterior part of the septum on 

 its right side, just above the anterior end of the base of the septal cusp of the 

 tricuspid valve. These auricular fibres (circular and septal) enter the central 

 fibrous body of the heart, which is situated between the aortic and the two : 

 auriculo-ventricular orifices. 



The nodal section is situated within the central fibrous body. It is a 

 small knot, consisting of an intricate network of muscular fibres, intermingled j 

 with, and embedded in, fibrous tissue. 



The ventricular section emerges from the nodal section as a single bundle, 

 which represents the main stem of the auriculo-ventricular bundle. This 

 stem passes forwards along the upper margin of the muscular portion of the 

 interventricular septum, lying immediately below the pars membranacea \ 

 septi, and beneath the anterior part of the base of the septal cusp of the 

 tricuspid valve. In this situation the main stem breaks up into two divisions? 

 — right and left. Each of these divisicms enters the septal wall of the corre-' 



