CERATODUS, PROTOPTERUS, AND CHIMERA. 495 



which bring blood into the heart, but shall confine myself to the structure of the heart 

 itself, more especially of the arterial cone. As a 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 " chordae tendinese," 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 annedens (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 

 rudimentai'y 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 Chwicera, and 

 have given a brief account, with figures, of the general architecture of the heart in the 

 three genera Chimcera, Ceratodus, and Frotopterus. 



I. Heart of Ceratodus. 



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 LXXXIII., 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 waUs 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 diagram matically the arterial cone and its longitudinal (and 



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