DR. A. GUNTHER’S DESCRIPTION OF CERATODUS. 
537 
venosum without valve ; this ostium is on the dorsal surface of the atrium, a little towards 
the right of its middle. A right and left vena cava superior , beside the principal vena 
cava , terminate in the sinus venosus, the former perforating the pericardium at nearly 
equal distances on the left and right from the mouth of the latter, which empties its 
contents a little towards the right of the median line of the end of the pericardium. 
The single vena pulmonalis does not communicate with the sinus, but, passing along its 
dorsal wall, enters the atrium by a separate opening more towards the left than the 
sinus ; its mouth is provided with a valve. The diameter of the vena pulmonalis is 
about equal to the sum of those of the two vense cavee superiores, and about one half of 
the vena cava. 
The conus arteriosus differs from that of Lepidosiren less externally than internally. 
Its anterior wall is thin, though provided with a muscular stratum, which is thickest 
along the posterior rim of its spiral course. Its beginning is indicated by the absence 
of trabeculae carneae, the inner surface being smooth. The valvular arrangement is 
entirely different from that which was considered to be the characteristic of the subclass 
Dipnoi. No valve exists on the boundary line between conus and ventricle. Before 
the conus turns to the left, its interior is rather spacious ; but this compartment is sepa- 
rated from the transverse portion of the conus by a cartilaginous valve, which from a 
certain view appears as a merely papillary prominence (d), but when viewed from vari- 
ous sides proves to be a spiral performing a half turn, to the lower end of which a 
muscle (d') is attached, which reaches down into the ventricle. This valve closes the 
lumen of the conus most effectually during the diastole of the heart. In the systole, 
the muscle attached to it contracts, and draws the valve from its position downwards, 
thus opening free egress to the blood out of the heart. When the muscle relaxes during 
the systole, the valve resumes its position through its own elasticity, shutting up the 
communication between the heart and arterial system. 
Beyond this valve the conus turns towards the left, and then for a very short distance 
forwards. Quite at the end of it, and immediately before it bifurcates, there are two 
pairs of (ganoid) valves ( e ), narrow, and rather long, with stiff non-collapsing walls, thicker 
along the middle than at the sides, and without tendinous chordae, in a single trans- 
verse series. Their tunics are continued in four narrow raised strips behind their 
bases * (/’). So far I have found the arrangement of this part of the heart nearly 
identical in two examples. On examining the first example, a pair of small papillary 
prominences (fig. 7, g') were found in a line between the series of stripes and the spiral 
valve, immediately in front of the latter. These stripes and papillse appeared to me to 
represent rudiments of a second and third series of valves, analogous to the plurality of 
series in other ganoid fishes. Remembering, at the same time, the fact that individual 
variations in the development and number of valves are not of uncommon occurrence in 
these fishes, I examined the heart of a second (smaller, female) specimen, and had the 
* Such longitudinal pads have been also found in Acanthias by Gegenbatje, Jena. Zeitschr. f. Med. und 
Naturwiss. ii. p. 366. 
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