282 



CLASS AMPHIBIA. 



spiral. There are two valves at the junction of the sinus and 

 right auricle, and two considerable valves at the margin of the 

 combined auriculo- ventricular apertures (Fig. 158). The latter 

 are held to the ventricular wall by cords, and there may be two 

 smaller additional valves. The auricles open into the left side, 

 and the conus arises from the right side of the ventricle, and 

 from that portion of it which is free from muscular strands 

 (Fig. 158). There is a row of three, sometimes four, semilunar 

 valves at each end of the conus (Fig. 157). The conus arteriosus 

 leads into a short ventral aorta (truncus arteriosus) which in 



A B 



Fig. 155. — A ventral, B dorsal view of the heart of a frog (after Gaupp). 1 line marking 

 the anterior limit of the pericardium ; 2 right auricle ; S conus arteriosus (bulbus cordis) ; 

 4 ventricle ; 6 sulcus coronarius marking the junction of the auricles and ventricle ; 6 truncus 

 arteriosus ; 7 left auricle ; 8 pulmono-cutaneous artery ; 9 aorta ; m common carotid : 

 11 pulmonary vein ; 12 sinus venosus ; 13 inferior vena cava ; 14 right superior vena 

 cava ; 16 left auricle. 



the Anura is divided into a dorsal and ventral chamber by a 

 horizontal partition. The branches of the ventral aorta are 

 bound together for a short distance in a common sheath. 



In the Gymnopkiona the conus is short, not spirally twisted, is without 

 a longitudinal valve, and in some species has only one row of valves. In 

 other Amphibia there is a row of valves at each end. In Proteus and 

 Menobranchus it is straight and without the longitudinal valve. The 

 longitudinal valve presents considerable variations, e.g. in the genus 

 Triton it may be present, or absent, or made up of a row of small processes. 

 a condition which suggests that it is really composed, as it is in Dipnoi, of 

 a row of small semilunar valves. It begins posteriorly close to one of the 



