THE HEART. 283 



of transverse, flattened bundles, which proceed chiefly ante- 

 riorly, but afterwards also superiorly and posteriorly, from one 

 auricle to the other, and are continued in them as transverse 

 fibres. 2. special fibres. These constitute, in the first place, 

 complete rings at the origins of the great veins, and at the 

 points of the appendices ; and, in the second place, a longi- 

 tudinal layer of some thickness beneath the endocardium } which 

 springs from the auriculo-ventricular openings, and is espe- 

 cially developed in the right auricle (musculi pectinati). Be- 

 sides these, there exist between the latter muscles, and also in 

 the auricles, numerous other small fasciculi, which, on account 

 of their irregularity, cannot be more particularly described. 

 The septum is to some extent common to both auricles. Its 

 muscles arise from the most anterior part of the upper border 

 of the septum of the ventricles, immediately behind the aorta, 

 from the posterior fibro-cartilage and arch to the right, around 

 the fossa ovalis, in which only slender fibres exist, in a superior 

 and posterior direction, in order to terminate, partly at the vena 

 cava inferior, partly by forming a complete ring ; whilst on the 

 left, they surround the fossa ovalis in the opposite direction. 



The muscular structure of the ventricles is disposed so that 

 on the external and internal surfaces the fibres everywhere 

 decussate; and in the intermediate portion, every stage of 

 transition from the one direction to the other is presented. 

 The muscular fibres arise at the ostia venosa and at the arterial 

 openings, in part immediately, and partly with the intervention 

 of short tendons, run more or less obliquely, (and some lon- 

 gitudinally or even transversely) and after they have sur- 

 rounded a portion of the ventricle in the longitudinal or 

 transverse direction, curve back again, and then terminate, 

 some in the musculi papillares, and chorda tendinece, whilst 

 others are again inserted in the points of origin above indi- 

 cated, so that without being interrupted by tendons, they 

 describe large involved loops or figure-of-8 turns of large size, 

 and running in very numerous and diverse directions. 



The endocardium is a whitish membrane, investing all the 

 elevations and depressions of the internal surface of the heart, 

 as well as the papillary muscles and their tendons, and the 

 valves. It is most developed in the left auricle (as much as J'"), 

 and thinnest in the ventricles, so that the muscular substance 



