550 PROF. E. R. LANKESTER ON THE HEART [Juiie 20, 



obvertitur et insidet margine iixo. Recte a Cuvierio maxima ex parte 

 carnea dieitur, quum noniiisi pars libera, anterior, margine leviter 

 concavo circumscripta, membraiiacea sit. Fasciculi musculares, 

 ad ipsam et e septo et e pariete antico teudentes ad tres ordines 

 reduci possunt. Inferior, major, e pluribus fasciculis componitur ex 

 septo medio infero ad extremum valvulae inferius abit, anterior ex 

 parietis anterioris parte inferiore recte ad basin valvulae ascendit, ubi 

 cum superiore, ex summitate septi descendente confluit." 



Owen, in the article Monotremata in Todd's Cyclopfedia, vol. iii. 

 p. 390, describes the valve somewhat differently. He distinguishes 

 two fleshy and two membranous portions — the smaller of the latter, 

 placed near the base of the pulmonary artery, agreeing according to 

 him with the smaller muscular fold of the Cursores, whilst the 

 second larger fleshy mass is homologous with the chief muscular 

 valve of the Bird's heart. 



Gegenbaur (" Zur vergleichenden Anatomic des Herzens," Jena- 

 ische Zeitschritt, 1866, vol. ii. p. 381) objects to this identification, 

 although he practically admits something very much like it in com- 

 paring the valve of Ornithorhynchiis to that of the Crocodile, which, in 

 its turn, may be readily shown to have common features with that of 

 the Bird. In his ' Elements of Comparative Anatomy,' English 

 edition, p. 584, Gegenbaur speaks of the fleshy structure of the 

 heart of Ornithorhynchus as being a retention in this animal of a 

 condition which is not unknown in other Mammalia, but is transient 

 in them, being found at an early period of development. 



In his memoir in the 'Jenaische Zeitschrift,' Gegenbaur gives 

 an original description of the right auriculo-ventricular valve of 

 Ornithorhynchus, but no figure of it. His description does not 

 agree with that of his predecessors, nor with what I have observed. 

 He says : — " I find the entire circumference of the right atrio-ven- 

 tricular ostium beset by a membranous valve, which has developed 

 muscular bundles only at certain parts, and is disposed, as the fol- 

 lowing account shows, somewhat otherwise than Meckel and Owen 

 have stated. Two portions may be distinguished in this valve 

 — a part adjacent to the ventricular septum, and a part which 

 fringes the ostium along the outer wall of the ventricle. The two 

 portions posteriorly pass into one another, and anteriorly, in the 

 neighbourhood of the origin of the pulmonary artery (that is, at the 

 conus arteriosus), are separated from one another, inasmuch as here a 

 spot is found in the circumference of the ostium in winch the valve 

 is interrupted." [This does not accord with the previous statement 

 as to the '• entire " circumference being beset with the valve. As will 

 be seen below, in the hearts examined by me a very large part of the 

 circumference of the ostium is devoid of any valve.] "The portion 

 of the valve corresponding to the outer ventricular wall begins broadly 

 at the conus arteriosus (or anteriorly) ; it stretches outwards and 

 backwards, becoming broader, and then narrows again and passes into 

 the median division of the valve. At the anterior point of fixation 

 of the valve, two strong muscular bundles pass from the ventricular 

 septum into the valve, and run (the heart being supposed to have its 



