CERATODUS, PROTOPTERUS, AND CHIMARA. 501 
constriction between conus and ventricle. The right auricular appendage presents a 
strongly marked additional lobe, which reaches far forwards (fig. 9, 7) 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 
auriculo-ventricular archway (AVV) 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 difference 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 trabeculze carnee—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 off cone 
from ventricle. The cone turns here with a sharp curve to the left, and then resumes 
its vertical course (see fig. 74). 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. 7B, 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, w/v), 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.—PART XI. No. 3.—February 1st, 1879. 3Y 
