288 



FRANKLIN P. MALL 



Fig. 26 Transverse .section. Embryo 16 mm. (No. 317). X 40. 



R.A. 







27 



■-^ 



Fig. 27 Coronal section through the heart of an embryo 21 mm. long (No. 460). 

 A square is around the atrio-ventricular muscle. 



