146 ON THE AIR-SACS OF THE CASSOWARY. [Mar. 2, 
pulmonary aponeurosis. The shape of the posterior air-sac’ is, 
however, rather different from that of the corresponding air-sac in 
Apteryx. Inthe latter bird, according to Prof. Huxley’s figure (oc. 
cit. figs. 1 and 2, v.), the posterior air-sac is rather smaller than the 
preceding posterior intermediate air-sac, and does not extend further 
back than the lung. In Casuarius the posterior air-sac forms ante- 
riorly a rounded capacious cavity, which pretty nearly corresponds in 
size to that of the posterior intermediate sac ; the cavity is, however, 
prolonged for some way backwards as a narrow interspace between 
the oblique septum and the parietes, but this posterior region is 
altogether outside the abdominal cavity and does not in the least 
resemble the condition of the posterior air-sac which is characteristic 
of the Carinatee. 
The pulmonary aponeurosis is thick, and costo-pulmonary muscles 
arising from the ribs are spread out over its surface; the oblique 
septum itself is stout and thick. 
Each lobe of the liver is contained in a separate compartment as 
in so many other birds (see P.Z.S. 1885, p. 836); the gizzard is 
enveloped in a special coat of peritoneum, while the intestines are 
covered below by a stout horizontal septum which laterally becomes 
indistinguishably fused with the oblique septum; in this respect 
therefore the Cassowary agrees with the Emu and with many 
Carinatee. Between the horizontal septum and the ventral peri- 
toneum wasa large mass of fat. 
The special resemblance between Casuarius and Apteryzx in the 
structure of the respiratory organs is not altogether in accord with 
the results obtained from the study of the structure of other organs. 
Prof. Garrod ! divides the Struthiones into three families, Apterya 
being the type of one ; Casuarius and Dromeus, Struthio and Rhea 
form the two other families. A study of the osteology has led Prof. 
Mivart® to a similar conclusion. The results contained in the 
present Note confirm the opinion expressed by these two authors 
that Casuarius and Rhea should be separated. I have not had the 
opportunity of examing the air-sacs of the Ostrich, but, judging from 
a sketch left by the late W. A. Forbes, they appear to be like those 
of Rhea. In Dromeus the air-sacs are not similar to those of 
Casuarius, but agree with Rhea in the extension of the posterior 
air-sac into the abdominal cavity. At the end of his paper *‘ On the 
Axial Skeleton of the Struthionide ” Prof. Mivart represents the 
affinities of the Struthious birds in a phylogenetic scheme. Removing 
Dromeus from Casuarius and placing it nearer to Rhea and Struthio, 
that scheme will exactly represent the position of the different genera 
of Struthiones as indicated by the structure of their respiratory 
organs. 
* Coll. Papers, p. 219. ? Trans. Zool. Soc, vol. x. p. 21. 
