554 PROF. E. R. LANKESTER ON THE HEART [June 20, 
ing to the septal part of the valve, are smaller in size, and in passing 
from left to right dwindle, so that at the right of the middle line the 
chordz are inserted directly into the ventricular wall and not into 
papillary eminences. Only three distinct papillary eminences can 
be distinguished in this series. 
Comparing this arrangement with that found in Man, it is obvious 
that the seven papillary muscles of the anterior part of the valve cor- 
respond to the “great”? and the “right” anterior papillary muscles of 
Man; whilst the superior series connected with the septal part of the 
valve correspond to the posterior papillary muscles of Man. But in the 
Rabbit not only must we consider that the “great” and the “right 4 
papillary muscles are divided and represented each by three separate 
papillary muscles, but also that the attachment of chorde springing 
from the extreme left of the left anterior cusp and from the left of 
the septal cusp in the human heart, are in the Rabbit attached to 
small papillary elevations of muscular substance, instead of being 
attached simply to the unraised surface of the ventricular wall. 
It is an interesting question as to whether the condition found in 
Man and in most mammals is more primitive than that found in the 
Rabbit. The fact that the Rodents are lower forms than the 
Simize might lead us to regard the condition seen in the Rabbit as 
more primitive ; but the very general conformity of the other Mam- 
malia (including such Marsupials and Edentata as have been examined) 
to the arrangement found in Man, leads to the supposition that the 
Rabbit’s right cardiac valve is a specialization departing from the 
earlier type preserved in Man. 
This conclusion will be found to be confirmed by the facts which 
we now shall expose in reference to the right cardiac valve of Ornitho- 
rhynchus. 
C. Or OrniTHoRHyYNCHUS PARADOXUS.—The right auriculo- 
ventricular valve of Ornithorhynchus is drawn in two sets of figures, 
accompanying this paper (Plates XXXIX., XL.), taken from the 
two female specimens in an excellent state of preservation mentioned 
above. In both of them the membranous collar which forms the 
complete valve in other Mammalia is seen to be incompletely de- 
veloped, and not “entire” as stated by Gegenbaur. Instead of the 
elliptical auriculo-ventricular orifice being completely fringed by the 
more or less deeply dependent valve, we find only its anterior margin 
and a small portion of its posterior or septal margin (the extreme 
right) thus fringed. The septal or posterior portion of the valve 
is, in fact, almost entirely wanting in one of my specimens (fig. 16). 
This result of my observations is diametrically in opposition to the 
statements of Gegenbaur quoted at the commencement of this memoir. 
The absence of the greater part, or even the whole, of the septal 
flap at once constitutes a very important difference between the right 
cardiac valve of Ornithorhynchus and that of any other Mammal 
which is known. 
Anterior flap —The well-developed anterior portion of the membra- 
nous valve is triangular in form, and is connected with a very large mus- 
cular column, which for convenience may be spoken of as musculus 
