404 



COMPARATIVE ANATOMY 



Neither in Urodela nor Anura is there a septum ventriculorum, 

 so that the blood passing out from the spongy ventricle must have a 

 mixed character (Fig. 306). The ventricle is usually short and 

 compressed, but is more elongated in Amphiuma, Proteus, and the 

 Gymnophiona. It is continued anteriorly into a conns arteriosus; 

 this has usually a slight spiral twist, and possesses a transverse 

 row of valves at either end, as well as a spiral fold, formed by a 

 fusion of valves and extending into its lumen, thus partially 

 dividing it into a dorsal cavum pulmonah, and a ventral cavum 

 aorticnm communicating with the carotid and systemic 



i.n. 



X.d 



Vcd, 



FIG. 307. HEART OF Cryptobranchus japonic^. From the ventral side. (After 

 Rose.) The left atrium is cut open. 



L.v, L.v 1 , the two pulmonary veins, opening by a single aperture into the left 

 atrium ; L. Vh, R. Vh, left and right atria ; O.ar, atrio- ventricular aperture ; 

 P.d and P.s, left and right pulmonary arteries; S.a, septum atriorum, 

 perforated by numerous small apertures ; tr, truncus arteriosus ; V.c.d 

 V.c.s, posterior cardinal veins; V.c.i, postcaval vein; V.j.d and V.j.x, 

 jugular veins; V.s.d and V.*.*, subclavian veins; l rt , 4", the four arterial 

 arches. 



arches. This holds good, e.g., for Ainblystoma, Salamandra, 

 Amphiuma, and Siren. In others (e.g. Necturus, Proteus, 

 Gymnophiona), the conus is more elongated, and reduction is 

 seen in the disappearance of the spiral fold and the presence of 

 only a single row of valves. 



In Anura, the fold lying within the conus extends so far back 

 that no undivided portion of the cavity is left. The consequence 

 of this is that the blood passing into the hindermost pair of the 

 arterial arches that from which the pulmonary arteries arise is 

 mainly venous, while the others contain more or less mixed blood 



