THE THORAX 



989 



that of the ventricles, the fibrous rings at the auriculo-ventricular orifices 

 inter\'ening between the two, and serving to connect them. 



Auricles. — The muscular fascicuU of the auricles are arranged in a super- 

 ficial set, common to both auricles, and a deep set, confined to each auricle. 

 The superficial fasciculi £ire disposed transversely, and some of them enter 

 the interauricular septum. They are best marked in front. The deep 

 fasciculi are arranged in two sets, looped Jind circular. The looped fasciculi 

 arch vertically over the auricle, their extremities being attached to the ring 

 of fibrous tissue which surrounds the auriculo-ventricular orifice. The circular 

 fasciculi are present in the auricular appendix, around the venous orifices, and 

 around the fossa ovaUs. The walls of the auricles, though muscular, are 

 thin. 



Ventricles. — ^The muscular fasciculi of the ventricles are. as stated, mostly 

 distinct from those of the auricles, and are disposed in a very complicated 

 manner. They spring, for the most part, from the rings of fibrous tissue 

 which surround the auriculo-ventricular orifices. The superficial fasciculi 

 descend obliquely towards the apex, where they are disposed in a twisted 

 or whorled manner, after which they pass on to the inner surface of the left 

 ventricle. Some of them become continuous with the musculi papillares 

 of that ventricle, whilst others ascend as a vertical layer on the inner surface 

 of the ventricle to be attached to the left auriculo-ventricular fibrous ring. 

 The superficial fasciculi are common to both ventricles. 



This figure is planned after 

 oae of Luschka's, but its 

 details were chiefly taken from 

 an original preparation. The 

 aorta, b', and pulmonary artery, 

 a', have been cut short close 

 to the semilunar valves, so as 

 to show the anterior fibres 

 of the auricles, a, superficial 

 layer of the fibres of the right 

 ventricle ; b, that of the left ; 

 c, c, anterior interventricular 

 groove ; d, right auricle ; d', 

 its appendix, both showing 

 chiefly perpendicular fibres ; 

 e, upper part of the left auricle ; 

 between e and b', the transverse 

 fibres which behind the aorta 

 pass across both auricles ; e", 

 appendix of left auricle ; /, 

 superior vena cava, around 

 which, near the auricle, circu- 

 lar fibres are seen ; g, g', right 

 and left pulmonarj- veins with 

 circular bands of fibres sur- 

 rounding them. 



Fig. 407. — Anterior View of He.\rt of a Young Subject dissected 

 AFTER Long Boiling, to show the Superficial Muscular Fibres 

 (Allen Thomson). §. (From Quain's 'Anatomy.') 



The remaining fasciculi are very numerous, and must be described sepa- 

 rately for each ventricle. The principal fascicuU of the left ventricle spring 

 from the left auriculo-vent.icular fibrous ring, and they pass more or less 

 obliquely towards the apex. In their course they turn" inwards, and enter 

 the front part of the interventricular septum inferiorlv. Some of them now 

 pass upwards to the base of the ventricle to be attached to the collection of 

 dease fibrous tissue, of the consistence of fibro-cartilage, already described ; 



