| OCR Text |
Show 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 (loc. 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 anteriorly 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 E m u and with many Carinatae. Between the horizontal septum and the ventral peritoneum 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 the Struthiones into three families, Apteryx being the type of one ; Casuarius and Dromceus, Struthio and Rhea form the two other families. A study of the osteology has led Prof. Mivart2 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 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 represents the affinities of the Struthious birds in a phylogenetic scheme. Removing Dromceus 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. 1 Coll. Papers, p. 219. 2 Trans. Zool. Soc. vol. x. p. 21. |
