SECT. 212.] OF THE HEART. 479 



bundles, which pass from one auricle to the other, continuing their 

 transverse direction, and are found especially on the anterior 

 aspect, but also superiorly and inferiorly. 2. Special fibres con- 

 fined to one auricle : some of these form true rings at the open- 

 ings of the great veins, and at the apices of the auricles; but 

 the mass of them form a pretty thick longitudinal layer beneath 

 the endocardium, arising from the ostia atrio-ventricularia, 

 and being particularly well marked in the right auricle, where 

 it forms the so-named musculi pectinati. Besides these fibres, 

 there also exist in the auricles, among those last mentioned, 

 numerous small bundles, which, from their irregular relation, 

 cannot be more minutely described. The dissepiment is, in part, 

 common to both auricles. Its muscular fibres arise from the 

 posterior fihrocartilage, situated at the front of the upper border 

 of the ventricular septum, immediately behind the aorta; thence 

 they proceed, on the right side, upwards and backwards, in an 

 arcuate manner around the fossa ovalis (in which only thin fibres 

 occur), and terminate partly upon the inferior cava, partly by 

 forming a complete ring round the fossa : on the left side, they 

 encircle the fossa ovalis in the opposite direction. 



The muscular fibres of the ventricles are so arranged, that those 

 of the outer and those of the inner surface everywhere proceed in 

 a decussating direction ; while between the two sets they present 

 more or less distinctly, all transitions of the one direction into the 

 other. The muscular fibres arise at the ostia venosa, and at the 

 mouths of the aorta and pulmonary artery, partly directly, partly 

 by means of short tendons ; they run more or less obliquely, but 

 some of them longitudinally or transversely; they bend round 

 again after they have encircled a section of the ventricle in the 

 longitudinal or transverse direction, and then terminate partly in 

 the musculi papillares and chordae tendinete, partly by becoming 

 attached again at the point from which they started. Thus, 

 without being interrupted by tendons, they describe large loops 

 or figures of eisrht running in very various directions, and almost 

 everywhere more or less twisted around themselves. 



The endocardium is a whitish membrane which invests all the 

 depressions and irregularities of the inner cardiac surface, as well 

 as the papillary muscles, their tendons, and the valves. It is best 

 developed in the left auricle, where it is a quarter of a line thick, and 

 is thinnest in the ventricles, so that in them the muscular sub- 

 stance appears through it of its natural colour. With regard to its 

 structure, it almost everywhere consists of three layers, an epithe- 



