MUSCULAR ARCHITECTURE OF THE HUMAN HEART 247 



valve of the aorta. In fact the floor of this valve is fleshy, unlike 

 that of the human. 



It is also noticed in the pig's heart that many of the circular 

 bands do not pass through the fleshy septum ])ut are attached to the 

 posterior ligament of the aorta and therefore do not make a com- 

 plete circle. This bundle is shown cut off under the thumb of the 

 left hand in fig. 19. In fact, there is a kind of raphe at this point 

 in the pig's heart which reaches through the heart wall to the base 

 of the posterior papillary muscle, and in a measure forms a break in 

 the main circular bands. This is noted to call especial attention to 

 a similar but much smaller group of muscle bundles around the left 

 ostium in the human heart. Its attachment is to the posterior 

 ligament of the aorta as shown in figs. 3, TR, and 8, TR. The 

 circular bundles extending partly around the left ostium have been 

 well pictured by MacCallum for the pig where they are very pro- 

 nounced.^- 



The extent of the deep Indlw-spiral l)and varies very much iji 

 different hearts. In the new-born and in young children this 

 band is very insignificant which indicates that during growth it 

 must enlarge faster than the other heart muscle l)undles. It also 

 varies in size in the adult heart. Figs. 5 to 12 are taken from an 

 hypertrophied heart which shows the circular bands markedly 

 thickened. On the other hand in a dilated heart with thin walls 

 it is barely present as fig. 13 shows. To show further variations 

 I add an illustration of a well-developed small heart in fig. 14. 

 Here the deep bulbo-spiral band is unusually well-developed, 

 in fact as well as in the hypertrophied heart shown in figs. 5 to 12. 



To show the course of the chief nmscle strands of the ventricles 

 of the heart, Schema B. is given. The bulbo-spiral bands are in 

 red and the sino-spiral in blue. The superficial l)ulbo-spiral band 

 roaches to the apex of the heart and there enters the septiun; 

 a layer somewhat deeper encircles the apex, while the middle 

 layer, the doej) bulbo-spiral, encircles the ventricle and ends with 



«2 MacCallum, I.e., fig. 20. MacCallum also fiiuis that the tice]) bull)o-si)ir;il 

 band arises not, only from the aortic septum but also from the tendon of the right 

 ostium venosum. Such an extension of the origin of this bundle beyond the aortic 

 septum does not exist either in the pig or in man. 



THE AMERICAN JOURNAL OF ANATOMY, VOL. 11, NO. 3. 



