[ 493 ] 
XIV. On the Hearts of Ceratodus, Protopterus, and Chimera, with an Account of unde- 
scribed Pocket Valves in the Conus arteriosus of Ceratodus and of Protopterus. 
By B. Ray Lanxesrer, VA., F.RS., Professor of Zoology and Comparative 
Anatomy in University College, London. 
Received May 28th, read June 4th, 1878. 
[Puates LXXXIII., LXXXIV.] 
INTRODUCTION. 
AMONG the numerous interesting structural features made known to zoologists by 
the admirable monograph of Dr. Giinther on the recently discovered Dipnoous form 
Ceratodus, none was more striking or more clearly indicative of the special zoological 
relationships of that remarkable animal than that exhibited by the arterial cone or 
basal portion of the arterial system. 
In describing this part of the heart of Ceratodus, Dr. Giinther says (Philosophical 
Transactions, 1871, p. 537):—* 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 trabecule carne, the inner surface being 
smooth. The valvular arrangement is entirely different from that which was consi- 
dered 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 separated from the transverse portion of the 
conus by a cartilaginous valve, which, from a certain view, appears as a merely papil- 
lary prominence, but when viewed from various sides proves to be a spiral performing 
a half turn, to the lower end of which a muscle 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 dis- 
tance forwards. Quite at the end of it, and immediately before it bifurcates, there 
are two pairs of (ganoid) valves, narrow and rather long, with stiff non-collapsing walls, 
thicker along the middle than at the sides, and without tendinous chorde, in a single 
VoL. X.—PART x1. No. £.—February 1st, 1879. 3X 
