40 ALLEN 
(Text-figs. 1 and 2, and Pl. VI, fig. 39; C.T.) and an inner coat 
composed of muscle bands, the ¢radbecule carne (Pl. V1, fig. 
39; T.C.A.). These muscle bands run in every direction, but 
mostly dorso-ventrad, and between these bands there are large 
blood cavities, which increase in size toward the central cavity, 
FIG. 1. 
the muscular layer becoming more and more compact toward 
the surface. The central cavity occupies a large portion of the 
auricle and is continued into the posterior lobes. Penetrating 
the floor of the auricle, a little caudad of the center, is the aurz- 
culo-ventricular opening (Pl. VI, fig. 39; A.V.O.), through 
