266 



FRANKLIN P. MALL 



Embryo No. 353 is 11 mm. long with a well formed arm and 

 hand plate. A profile outline of the embryo may be seen in the 

 figure by Evans. 13 The sections are 10/j, thick in a coronal direc- 

 tion and slightly oblique, that is, they strike the heart transversely. 

 The heart which has been modeled in wax is 1.7 mm. wide and 2.2 

 mm. long. The apex is cleft as is so often the case in this stage of 

 development. 14 The septum aorto pulmonale is complete and the 

 anterior and posterior cushions are fully united into a single mass 



Fig. 11 View from below of a model of the hear! of an embryo 11 mm. long (No. 

 353). X 50. The ventricles have been cutoff. The connective tissue septa are 

 colored yellow. 



of connective tissue. This mass extends to a point up in the atrial 

 septum on its dorsal side, to the left valve of the opening into 

 the sinus venosus. The complete union of the two cushions has 

 obliterated the foramen ovale I and the foramen ovale II is well 

 above the common fibrous process of the united cushions. A 

 view from below, that is after the apex of the heart is cut off, 



13 Evans, Keibel-Mall Handbuch, Bd. 2, fig. 469. 



14 Mall, Bifid apex in the human heart. Anat. Rec, vol. G, 1912. 



