550 PROF. E. R. LANKESTER ON THE HEART [June 20, 
obvertitur et insidet margine fixo. Recte a Cuvierio maxima ex parte 
carnea dicitur, quum nonnisi pars libera, anterior, margine leviter 
concavo circumscripta, membranacea sit. Fasciculi musculares, 
ad ipsam et e septo et e pariete antico tendentes ad tres ordines 
reduci possunt. Inferior, major, e pluribus fasciculis componitur ex 
septo medio infero ad extremum valvule inferius abit, anterior ex 
parietis anterioris parte inferiore recte ad basin valvule ascendit, ubi 
cum superiore, ex summitate septi descendente confluit.”’ 
Owen, in the article Monotremata in Todd’s Cyclopzedia, 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 Anatomie des Herzens,” Jena- 
ische Zeitschrift, 1866, vol. ii. p. 381) objects to this identification, 
although he practically admits something very much like it in com- 
paring the valve of Ornithorhynchus 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 ove another, inasmuch as here a 
spot is found in the circumference of the ostium in which 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 
