202 Kathleen K. Oliver: 



the synangial valves in regulating the blood tlow through the 

 Truncus. 



On the right hand wall of the Truncus a definite, papilla-like 

 structure is present (p), and opposite it on the same side of 

 the fold is a depression (d), into which the papilla fits. Bourne, 

 in his work on Rana, states that the Pulmo-cutaneous arch 

 opens from the Synangium, anterior to the spiral valve and its 

 attendant synangial valves ; also he figures the valves as facing 

 up towards the cavity of the Synangium. 



The synangial valves in the Australian frogs that I have in- 

 vestigated are between the Pulmo-cutaneous arch and the Syn- 

 angium, and this position, togetlier with the presence of the in- 

 terlocking apparatus, would suggest the following theory as to 

 the regulation of the blood flow through the Truncus — that 

 when the spiral valve is in its normal position — that is, the 

 position in which there is least pressure exerted on it — and this 

 is when the pressure is greatest in the Synangium, and therefore 

 lower in the Pylangium, the interlocking apparatus is closed, the 

 papilla on the Pylangial wall fitting closely into the depression 

 on the spiral valve. In this position the spiral valve would 

 direct the impure blood, entering first on the Ventricular Sys- 

 tole to the left, and so on up to the Pulmo-cutaneous arch, 

 where the pressure is lowest, the preceding systole having forced 

 the blood on to the lungs. When the Pylangium is full, and 

 the pressure becomes greater than that above in the Synangium, 

 the blood forces up the Synangial valves, and these, being 

 fused with the spiral valve, pull the fold over to the left, thereby 

 opening the interlocking apparatus, and the blood rushes to- 

 wards the Systemic and Carotid area, there being now less 

 pressure than in the Pulmo-cutaneous entrance. 



CYyTlGNATHIDAB. 



1. Limuodyiutxtei^ dorsalis. (Plate XXXVITI., Figs. 9-10.) 



In LimnodynnMes dorsalis there are two very distinct synan- 

 gial valves (Fig. 9 viv2). The valve attached to the left side of 

 the Truncus is large, semi-lunar, and definite, and that further 

 to the right is smaller, its right hand end fusing with the 

 anterior end of the spiral valve. Both valves have their cups 



