328 BRUNER. [Vol. XVI. 



ture of the entire region. This fact explains the manner in 

 which the vein projects into the atrial cavity (see PI. XV, Fig. 3). 



The sinus-atrium opening of amphibians is furnished, in typi- 

 cal cases (Perennibranchiata), with two transversely placed valves, 

 which are attached on the right to the atrial wall, on the left to 

 the septum atriorum. In Salamandrinae, however, one of these 

 valves, the ventral one, becomes rudimentary or wholly disap- 

 pears, while the other is greatly enlarged. The form and rela- 

 tions of the latter valve in Salamandra are shown in PI. XV, 

 Figs. I, 3, and 4. In this species a second valve is wholly 

 wanting. The enlarged valve is a sail-shaped membrane, which 

 extends from the sinus-atrium opening to the atrio-ventricular 

 opening, where it is attached, along with the septum atriorum, 

 to the middle of the inferior valve. The convex margin of the 

 valve is fixed by means of muscular trabeculae to the septum ; 

 the concave margin is wholly free. The attachment of the 

 dorsal end of the valve follows the ventral wall of the pulmo- 

 nary vein from the septum to the sinus opening, where the valve 

 bends toward the right, covers the opening, and attaches to its 

 dorsal half. 



The sinus valve, like the septum and atrial walls, is contrac- 

 tile, its muscular bundles being in part continuous with those 

 of the supporting structures. In the neighborhood of the sinus 

 opening these bundles are strongly developed in a dorso-ventral 

 direction, which is here the direction of greatest tension. 



The truncus arteriosus projects forward from the ventricle 

 with a slightly sigmoid curve. Its proximal portion (conus 

 arteriosus) contains two circles of valves — a posterior one, 

 which lies at the ventricular opening and consists of three 

 pouches, and an anterior set, which includes normally four 

 valves. One of the valves of the distal circle is produced cau- 

 dalward as a low ridge of connective tissue, which terminates 

 in front of the proximal set of valves. This ridge is the 

 so-called spiral fold of the salamander. 



Beyond the conus we find the bulbus arteriosus, from which 

 arise the great arterial trunks. 



With the foregoing description as a basis for comparison, we 

 may now turn to the study of salamanders without lungs. 



