CEEATODUS, PKOTOPTEEUS, AND CHIM^BA. 501 



constriction between conns and ventricle. The right auricular appendage presents a 

 strongly marked additional lobe, which reaches far forwards (fig. 9, x) and renders the 

 auricle asymmetrical. The dotted line on the surface of fig. 9 indicates the direction 

 of the cut by which the appearances in fig. 10 were obtained. 



The sinus and median portion of the auricle have been opened by a cut along the 

 median dorsal line, and the cut edges pinned back (fig. 10). The floor of the sinus is 

 seen to be fibrous and tough. In front the walls become more delicate, and are turned 

 in so as to present two folds (Sav), which are inserted into the fibro-cartilage {FC). 

 These folds indicate the separation between sinus and auricle, and serve as valves. 

 The head of the great basilar fibro-cartilage (FC) is seen projecting from beneath the 

 aui-iculo-ventricular archway (AW) into the auricle. It terminates in a point, from 

 which the septal folds take origin. 



The dotted line on fig. 8 indicates the direction of a cut by which the whole length 

 of the ventricle and conus arteriosus was divided so as fully to expose their cavities, the 

 cut edges being pinned back. The resulting appearances are given in fig. 11, which 

 presents a view of the heart of Protopterus very closely similar to that of the heart 

 of Ceratodus given in fig. 3. The chief difi'erence depends upon the fact that the upper 

 limb of the conus of the Protopterus heart has been completely bisected. The very 

 small ventricular cavity and the very thick ventricular walls are remarkable ; arising 

 from the floor of the ventricular cavity we have the ventricular extremity of the basal 

 fibro-cartilage {FC). We here see it disappearing beneath the auriculo-ventricular 

 curtain or archway, just as (in fig. 10) we see it emerging from beneath the same screen 

 on the auricular side. The auriculo-ventricular curtain valve is seen to be the extended 

 inferior margin of the conus arteriosus, as it is in Ceratodus, and can be traced on the 

 right-hand side of the figure into trabeculae carneae — with which compare the similar 

 disposition in Ceratodus (fig. 3). On the left-hand side of the lower segment of the 

 conus arteriosus, as thus exposed, we see a broad fleshy fold which has a free slightly 

 incurved lower margin. This is the longitudinal valve. The arrow indicates the hidden 

 course of the transverse segment of the arterial cone. This region is indicated in the 

 surface-view of the heart by the dilated region above the constriction marking ofi" cone 

 from ventricle. The cone turns here with a sharp curve to the left, and then resumes 

 its vertical course (see fig. 7 a). The longitudinal valve does not, however, terminate 

 in this region as in Ceratodus, but is continued along the upper vertical segment of the 

 cone (fig. 7 b, and fig. 11, Sp. v). In this upper region only it is accompanied by a second 

 longitudinal production of the wall of the conus (fig. 10, ulv), which is of a denser 

 substance, and is more probably to be regarded as a septum than as a muscular valve, 

 such as the longer spirally-turning fold certainly is. No trace of " ganoid " valves 

 such as those of Ceratodus, are to be found in the upper segment of the heart of Pro- 

 topterus. The continuation of the spiral valve and the second septal fold entirely 

 replace them. 



VOL. X. — PAKT XI. No. 3. — February \st, 1879. 3t 



