270 TEXT-BOOK OF PHYSIOLOGY 



The arrangement of the muscle-fibers is quite complicated and in ac- 

 cordance with the -functions of the individual portions of the heart. In 

 the auricles the fibers are arranged in two sets: an outer transverse set, 

 which pass from auricle to auricle, and an inner longitudinal set, which 

 pass over the auricles and are attached anteriorly and posteriorly to the 

 connective tissue of the transverse auriculo-ventricular septum. The longi- 

 tudinal fibers of the auricles are practically independent of each other. 

 Circularly arranged fibers are present near the terminations of the venae 

 cavae and pulmonic veins. 



In the ventricles the muscle-fibers are also arranged in two sets, a 

 superficial longitudinal and a deep transverse, though their arrangement is 

 somewhat more complicated than that observed in the auricles. In a 

 general way jt may be said that the superficial longitudinal fibers on both 

 the anterior and posterior surfaces take their origin in the connective tissue 

 of the auriculo-ventricular septum. The superficial fibers on the anterior 

 surface of the heart pass obliquely downward and forward from right to left 

 toward the apex, where they turn backward and inward in a vertical manner 

 after which they ascend to terminate in the wall of the septum, the columnae 



i ii 



FIG. 114. ARRANGEMENT OF VENTRICULAR MUSCLE-FIBERS. (After MacCallum.) I and 

 II, Superficial fibers of the left ventricle and conus arteriosus; III, deep layers of the left ven- 

 tricle; LAV, mitral orifice ; RAV, tricuspid orifice; PA, pulmonic artery. (From Hirschf elder.) 



carneae and musculi papillares. The superficial fibers of the posterior sur- 

 face of the heart pass obliquely downward from left to right, wind around 

 the apex, turn upward and end in the same structures as do the fibers from 

 the anterior surface. The fibers from the base of the right ventricle termi- 

 nate in the structures of the left ventricle, while those from the left ventricle 

 terminate in the structures of the right ventricle. Longitudinal fibers are 

 also found on the inner surface. The transverse fibers are very abundant 

 and surround each ventricle separately though they are continuous with 

 each other across the septum. Between the superficial longitudinal and deep 

 transverse fibers there are several layers of fibers which possess varying 

 degrees of obliquity. The general arrangement of the fibers is such as to 

 insure a complete and simultaneous discharge of blood from both auricles 

 as well as from both ventricles (Fig. 114). 



THE MUSCLE CONNECTION BETWEEN THE AURICLES AND 



VENTRICLES 



The Muscle Band of His, or the Auriculo-ventricular Bundle. In 

 the mammalian heart there is no continuity of the muscle-fibers across the 



