230 ON THE OBLIQUE SEPTA IN THE PASSERINES, [Feb. 4, 
of that reptile are invested by a closely adherent membrane, which 
has been thus described by Prof. Huxley ':—‘ A fibrous expansion 
extends from the vertebral column over the anterior face of the 
stomach, the liver, and the dorsal and front aspect of the 
pericardium, to the sternum and the parietes of the thorax, 
separating the thoraco-abdominal space into a respiratory and a 
cardio-abdominal cavity, and representing the oblique septum of 
the bird.” Both I? and Mr. G. W. Butler * have included in the 
comparison which Prof. Huxley thus made the omentum of the 
bird. But this does not interfere with the special likeness which 
the Passerine shows to the Crocodile, in that the representative of 
the oblique septum of other birds has not (as a rule) a ventral 
attachment on each side to the sternum, but that it forms a 
closely investing sheath to the liver-lobes ; but it is very doubtful 
whether this resemblance is more than a superficial one. It is 
agreed on all hands that the Passeres are a much, if not the most, 
specialized group of birds, standing on the very topmost branch of 
the avian tree. Among them, therefore, the retention of archaic 
characters, though possible, would not be so likely as among some 
other groups. Besides, the arrangement of the oblique septa in 
them seems to be a secondary affair on account of the fact that the 
original (?) position of the attachment of those septa is indicated 
by rudiments varying in degree of the portion of the septa which 
was formerly inserted laterally and ventrally on to the sternum, 
and the Rook has these membranes complete. This may be in the 
form of a much-fenestrated membrane, or there may be but a single 
tag on each side near to the posterior margin of the sternum, or, as 
in an example of Prosthemadera nove-zealandie, the attachment 
may have been completely retained on one side. I should be dis- 
posed, therefore, in spite of certain undeniable likenesses which 
the Passerines show to the Crocodilia, to regard the relations of 
the oblique septa in them as a modification of the more prevalent 
disposition of those parts. 
In describing the septa of the somewhat aberrant Australian 
Struthidea, I called attention to the fact that the liver-lobes were 
partly shut off from the subomental space by membranous 
partitions. The exact way in which these partitions are related to 
the liver-lobes is, so far as my experience goes, unique among birds. 
But there are other birds in which an arrangement of the same kind 
exists ; but with certain differences. 
In several birds, for instance in Chrysotis guildingi, the left liver- 
lobe is completely shut off from the subomental space by a vertical 
transverse partition ; there is no corresponding partition on the 
opposite side of the body. There are some birds in which, as in 
Struthidea, there are partitions on both sides; but in them the 
partitions are quite complete and entirely shut off the liver-lobes 
from the subomental space, not merely partially as in Struthidea. 
1 Loe. cit. p. 568. 
2 “On the Respiratory Organs in certain Diving Birds,” P. Z.8. 1888, p. 256. 
* On the Subdivision of the Body-cavity in Lizards &c.,” P. Z. 8, 1889, p. 453, 
