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FRANKLIN P. MALL 



inferior septum which is just beginning to form from below and 

 behind (fig. 33). Thus it is seen that the vortex of the apex is 

 laid down in the heart of an embryo 10 mm. long (fig. 32). 



In a set of perfect serial sections of the heart of an embryo 



32 

 Fig. 31 Outline drawing of the front of the heart of an embryo 10 mm. long (No- 

 426). The course of the fibers is indicated. 

 Fig. 32 The same heart, viewed from below. 

 Fig. 33 The same heart, viewed from behind. 



11 mm. long (353) no such interlacing of the fibers can be seen, 

 excepting well up near the base of the heart where the fibers from 

 the right side cross over the anterior longitudinal furrow, while 



