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XIV, On the Hearts of Ceratodus, Protopterus, and Chimsera, with an Account ofunde- 

 scrihed Pocket Valves in the Conus arteriosus of Ceratodus and of Protopterus. 

 By E. Kay Lankester, M.A., F.B.S., Professor of Zoology and Comparative 

 Anatomy in University College, London. 



Received May 28th, read June 4th, 1878. 



[Plates 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 oi 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 trabeculse carnese, 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 chordae, in a single 



VOL. X. — PART XI. No. 2. — February \st, 1879. 3x 



