DEVELOPMENT OF THE HUMAN HEART 



297 



loops now form the anterior horn of the vortex and the lower end 

 of the loops form the posterior horn. 40 



To sum up : The simple heart tube is made up of circular fibers 

 which in a general way remain circular throughout development. 

 After the heart is well kinked upon itself the fiber bundles around 



35 



36 37 



Fig. 34 Course of the fibers in the heart of an embryo 17 mm. long. The view is 

 from behind. 



Fig. 35 The same as fig. 34 from the heart of an embryo 25 mm. long. The fibers 

 which pass to the base on the right ventricle are present. 



Fig. 36 The same as fig. 35, from an embryo 27 mm. long. 



Fig. 37 The same as fig. 35, from another embryo 27 mm. long (Xo. 33). 



the venous and arterial ends remain circular but there are marked 

 deviations at the apex which correspond with the kinking at this 

 point. Those fibers that arise from the bulbo-ventricular groove 

 in front encircle the left ventricle and enter the ventricular sep- 



40 His, Anat., mensch. Embryonen, Bd. 3, S. 177, makes a statement which is 

 just the opposite of mine. • 



