THE CIRCULATION 



213 



3rd. The inmost layer is continuous with the outmost layer, 

 as it turns in at the apex. It may be considered as composed 

 of two parts 



(a) A layer of fibres running longitudinally along the in- 

 side of each ventricle from the apex upwards to the auriculo- 

 ventricular ring. These fibres are raised into fleshy columns, 

 the columnse carneae. 



(6) A set of fibres, constituting the papillary muscles 

 (Fig. 107, P.M.), which, taking origin from the apical part of 

 the ventricles, extend freely upwards to terminate in a series 



\FlG. ],OG. Cross Section thrjaugfr the Ventricles of thfi__He.act looking towards 



Auricles, to show the right Ventricle placed on the Central Core of the left 

 Ventricle. The cusps of the Auriculo-ventricular Valves are also shown. 



of tendinous cords (the chordae tendineae), which are inserted 

 partly into the auriculo-ventricular valves, presently to be 

 described, and partly into the auriculo-ventricular rings. 

 The papillary muscles are merely specially modified columme 

 carnese. In many cases, actual muscular processes extend 

 from the apex of the papillary muscles to the auriculo- 

 ventricular ring. 



In the left ventricle there are two papillary muscles, or 

 groups of papillary muscles, one in connection with the 

 anterior wall of the ventricle, called the anterior muscle; 

 and one in connection with the posterior wall, called the 

 posterior muscle. 



In the right ventricle there are 1st. One or more small 



