CERATODUS, PROTOPTERUS, AND CHIMARA. 495 
which bring blood into the heart, but shall confine myself to the structure of the heart 
itself, more especially of the arterial cone. Asa chief result I show that there exist 
in the lower part of the arterial cone of Ceratodus a numerous series of small and deli- 
cate “ ganoid” or “ pocket” valves provided with “ chord tendinex,” which valves have 
not been described by Dr. Giinther as occurring in the two hearts studied by him. And 
further, led by the observation of this “lower-end” series of valves to examine the 
corresponding region in the heart of Protopterus annectens (of which species the Museum 
of University College contains several fine examples bequeathed by the late Professor 
Grant), I have arrived at the interesting result that the Protopterina, as well as 
the Ceratodontina, possess “ ganoid” valves in the conus arteriosus, though in a 
rudimentary condition. Accordingly the absolute distinction between the subfamilies 
Ceratodontina and Protopterina, based on the presence and absence respectively of 
these valves, breaks down, although the spirit of the distinction, which consists in the 
more complete substitution of “longitudinal” valves for “ pocket” valves in Proto- 
pterina, as compared with Ceratodontina, remains. Lastly, I have examined the struc- 
ture of the heart in the fish most closely related to the Dipnoi, namely Chimera, and 
have given a brief account, with figures, of the general architecture of the heart in the 
three genera Chimera, Ceratodus, and Protopterus. 
I. Heart or Creratopvs. 
A view of the heart of Ceratodus, as seen when removed from the pericardium, with 
the right side facing the observer, is given in Plate LXXXIIL., figure 1. The heart is 
chiefly remarkable for the great bulk and solidity of the conus arteriosus, from which the 
branchial vessels spring like a stack of chimneys. The fleshy ventricle comes to a 
point in the middle line (here turned to the right); and from this apex a fibrous band 
extends to the pericardium. The auricle has much thinner walls than either ventricle 
or conus. It is not possible to distinguish on the surface (nor indeed interiorly) 
a demarcation between auricle and sinus venosus. This fact is not alluded to by 
Dr. Giinther, but is important, because in Protopterus and, according to Hyrtl, 
in Lepidosiren an internal separation of auricle and sinus can be observed and a 
corresponding external constriction. 
On the surface of fig. 1 the dotted line represents the direction of the cut which 
was made so as to obtain the view given in fig. 2. By this cut the cavity of the 
ventricle is thrown open; a flap, constituting its right wall, is thrown back. At the 
same time the upper part of the conus arteriosus is opened, and the cut edges of its 
muscular walls are divaricated so as to exhibit the valves which lie within it. The 
lower part of the arterial cone, which is twisted so as to lie in a different plane from 
the upper part, and which connects the upper part with the cavity of the ventricle, has 
not yet been cut into. The figures of dissections will be best understood if the draw- 
ing fig. 7A, representing diagrammatically the arterial cone and its longitudinal (and 
3x 2 
