94 
JANE I. EOBEliTSON. 
Text-fig. 15. 
B. 
F. 
Serial sections (transverse) through the heart of Lepidosiren 
at Stage 31. a. Through the anterior part of the ventricle. 
Note continuity of the auriculo- ventricular ridge {av. r.) with 
the ventricular musculature. B. Through the posterior region 
of the ventricle, c. Through the auricles, d. Anterior to the 
