1882. ] OF ORNITHORHYNCHUS PARADOXUS. 551 
apex directed backwards) in a nearly horizontal direction in the 
valve. They occupy, however, scarcely the third part of the entire 
length of this division of the valve. At the broadest part of this 
same division a muscular band passes from the ventricular septum, 
and is inserted into the former, and spreads its fibres in a fan-like 
expanse in the valve nearly up to the origin of the valve from the 
margin of the ostium. A second smaller bundle lies behind this, 
also arising from the septum. If we spread out the valve, and 
compare the purely membranous surface with that provided with 
muscular tissue, the former is found to be larger than the latter. 
The second portion of the valve arises from the part of the ostium 
belonging to the septum. At its narrower part it is in continuity 
with the other division of the valve, broadens out from behind 
forwards, and is fastened to the septum along a perpendicular line 
stretching from the ostium into the ventricle. It is therefore not 
only fastened to the circumference of the ostium, but, starting from 
there, also to the septum. Since the latter line of fixation is per- 
pendicular to the line of origin along the ostium, this portion of 
the valve forms a ‘ pocket-valve ’"—the more so since no trabeculee 
pass to its free margin, and moreover no muscular fibres can be 
detected in its substance. 
“ When a comparison of this arrangement is made with that of 
Birds, the difficulty is at once obvious that in Ornithorhynchus the 
septal portion of the ostium has a valve, whilst such is wanting in 
Birds. The whole apparatus cannot, therefore, be compared with 
that of Birds, but only the portion of the valve which arises from 
the outer half of the circumference of the ostium.” 
In the absence of figures it is not possible fully to comprehend 
Professor Gegenbaur’s description ; but it seems to me probable that 
the heart examined by him differed individually from those studied 
by Meckel and Cuvier, aud from the two examined by me. In these 
two, as will be seen below, considerable differences were observed on 
comparison one with another. 
The main point on which Gegenbaur insists, is the existence of 
a septal portion to the valve; it is on this account that he objects 
to a comparison with the Bird’s valve. But this septal portion seems 
to have been exceptionally large in the heart studied by him. In 
both my specimens it was small, and left the /arger part of the 
septal margin of the ostium unprovided with any valvular fold. At 
the same time it was larger in one specimen than in the other. The 
existence of a greater or less portion of the valve along the septal side 
of the ostium does not appear to invalidate the comparison of the 
main bulk of the valvular structure with that of the Bird’s heart, 
though the closeness of the agreement is diminished by the fact 
insisted on by Gegenbaur, viz. that the muscular bands of the valve 
arise in Ornithorhynchus, as in the Crocodile, from the septal wall 
of the ventricle, and not from the free outer wall as in the Birds. 
Recognizing, as all anatomists must do, the great interest attach- 
ing to the observation that in Ornithorhynchus muscular tissue to a 
large extent invades and replaces the membranous structure which 
Proc. Zoou. Soc.—1882, No. XXXVII. 37 
