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Show 1876.] ANATOMY OF CHAUNA DERBIANA. 193 to the bronchi, the Screamers are not Anserine, and in the latter feature peculiar. There is nothing remarkable in the rings of the windpipe, their interlocking producing the well-known key-pattern. The last two are greatly compressed laterally, so that the membranous bronchi, in each of which there are only a very few slender half-rings, arise quite close together. As can be seen from the figure, Plate XII. figs. 2, 3, 4, the lateral muscles of the trachea are peculiarly powerful; the upper extrinsic pair is inserted into the middle of the membrane which runs between the body of the coracoid bone and the corresponding limb of the furcula on each side; the lower close to the costal process of the sternum, at the back of the sterno-coracoid articular margin of the former bone. The intrinsic muscle on each side descends the windpipe to end by bifurcating opposite the origin of the sterno-tracheal muscle, and cease, its anterior portion higher than its posterior, six or seven rings lower down, some distance above the bifurcation of the bronchi. The above-mentioned extremely delicate nature of the commencing bronchial tubes is most peculiar. The lungs present no special features of interest. There are several myological characters which, though small in themselves, all go to form the exact definition of any group of birds, and aid in the determination of affinities. Among the more important of these are the presence or absence of the ambiens muscle* (which is of fair size in Chauna), the presence or absence of the femoro-caudal, the semitendinosus, and their accessory heads (which are all four found in Chauna). Having dwelt fully on the importance of these muscles in the paper just referred to, all I need remark on the present occasion with regard to them is, that there is therefore a difference between this bird and all the true anserine birds, in none of which is there ever a trace of the accessory semitendinosus. A reference to m y paper on the muscles of the thigh of birds will show that in possessing all the five above-mentioned muscles the Screamers agree only with the Gallinae and their nearest allies, the Rallidae, Musophagidae, Cuculidae, Columbae, and some of the Limicola?. With reference to secondary myological points, there are four which, in my estimation, deserve special attention. They are :- 1. The presence or absence of the expansor secundariorum muscle. 2. The presence or absence of a special muscular slip from the biceps humeri to the patagium. 3. The area of origin of the obturator internus. 4. The degree of development of the tensor-cruris fascia. These will be considered separately. 1. The presence or absence of the Expansor secundariorum muscle. Expansor secundariorum is the name which it is m y habit to employ for a very small and peculiar triangular muscle arising from the quills of the last few (generally two or three) secondary * Vide P. Z. S. 1874, p. 116. P R O C ZOOL. Soc-1876, No. XIII. 13 |