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. In the latter bird, according to Prof. Huxley's figure (Joe. 

 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 Carinatae. 



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 

 Carinatae. Between the horizontal septum and the ventral peri- 

 toneum was a large mass of fat. 



The special resemblance between Casuarius and Apteryx 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 tlie Struthiones into three faniilie^i, Apterya' 

 being the type of one ; Casuarius and Dromceus, 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 examiug the air-sacs oftlie Ostrich, but, judging from 

 a sketch left by the late W. A. Forbes, they appear to be like those 

 of Rhea. In Dromceus 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 Struthionidae " Prof. Mivart ret)resents tbe 

 aflSnities of the Struthious birds in a phylogenetic scheme. Removing 

 BromcEusirom Casuarius and placing it nearer to Rhea andStruthio, 

 that scheme will exactly represent the position of the different genera 

 of Struthiones as indicated by the structure of their respiratory 

 organs. 



' OoU. Papers, p. 219. ^ Trans. Zool. Soc. vol. x. p. 21. 



