102 
JANE I. KOBERTSON. 
first and third ridges, while in the proximal part three little 
cushions (fig. 20d, e7i. c.) appears on the posterior (dorsal) and 
lateral walls. Ridge 4 tends to become fused with ridge 1 and 
in two specimens could only be traced at intervals, the wjills 
of the bulbus being occupied by the ridges 1, 2 and 3. The 
additional second and fourth ridges disappear with the 
general flattening of the bulbar lining that soon follows, but 
the little secondary cushions in the proximal part remain and 
Text-fig. 20. 
BR... 
Serial sections (transverse) through the heart of Lepidosiren 
at Stage 34. a. Through the distal end of the bulbus cordis. 
B. Through the transverse segment of the bulbus. Note the 
continuity of the ridge (B. B. A.) on the anterior (ventral) wall 
of the proximal segment of the bulbus, along the transverse 
segment with the right bulbus ridge (R. B. 1). c. Through 
the posterior part of the transverse segment of the bulbus. 
D. Through the proximal end of the proximal segment of the 
bulbus. B. B. 1. Right bulbus ridge. B. B. 2. Posterior 
temporary ridge. B. B. 3. Left bulbus ridge. B. B. 4. 
anterior temporary ridge. B. B. A. Ridge on the anterior 
(ventral) wall of the proximal segment of the bulbus. er?. c. 
En docardial cushions of rudimentary pocket- valves. 
are visible in the adult, where they form the rudimentary 
pocket-valves. The right and left ridges (B. B. 1 and B. R. 3) 
and the a ridge persist as the septa of the adult bulbus, 
ridges 1 and A forming together the spiral valve. 
