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Show 112 MR. A. H. GARROD ON THE MUSCLES OF BIRDS. [Feb. 3, types of muscular arrangement in the thighs of birds, as far as the four muscles now under consideration are concerned. Each of the circles in the diagram is divided into two halves^ by a vertical line, so that the names of all those birds which are found to possess the ambiens muscle may be distinguished from those m which it is absent. The birds in which the ambiens is present are placed in the left-hand semicircles; those in which it is absent are to be found in the right-hand semicircles. m A few examples may illustrate the method of employing this table. Taking the Musophagida, for instance, they being found in the circle A B. X Y evidently possess all the four muscles-the femoro-caudal, the accessory femoro-caudal, the semitendinosus, and the accessory semitendinosus; and being on the left side, have also the ambiens. The Strigida being on the right side of the circle with the formula A possess only the femoro-caudal, the ambiens being also absent; and so on. those birds whose names appear partly in both semicircles may or may not possess the ambiens muscle in their different genera. . c Before going further it will be necessary to show what degree ot constancy is, as a rule, to be expected in the myology of birds. Respecting this point m y experience is that individuals of a species agree precisely in their muscular arrangement. Many specimens of a considerable number of species have passed through my hands, and I have frequently dissected them one after another in order to detect, if possible, any individual variations; such, however, have not been forthcoming. It is true that in a single specimen of (Edi-cnemus grallarius the ambiens, instead of crossing the knee, ended on the inner side of the ligamentum patellae ; however, the muscle, though imperfectly developed, was undoubtedly there. The only other instance of an unexpected and abnormal individual structure was the presence in a specimen of Pomatorhinus temporalis, on one side only, of an accessory femoro-caudal, which I have not once seen in any other of at least 100 passerine birds that I have examined. From these observations it is evident that individuals of a species all agree in the arrangement of the muscles of the thigh at least- so much so that any peculiarity observed in a specimen dissected for the first time may be taken to be characteristic of the species itself. The same remarks apply to the species of a genus. Of several genera I have had the opportunity of dissecting many species, seven of Bubo, six of Ardea and Columba, five of Buceros, Francolinus and Ibis, four of Chrysotis, Brotogerys, and Geopelia, three of a large number, and two of many more. In all these genera the myology of the species does not vary, and its constancy is sufficient to justify the suspicion that when there are muscular differences between the species of an accepted genus, it is because genera have been combined which ought to be kept distinct. Such is evidently the case with Conurus, in which genus those without the red tail differ from those possessing it (Pyrrhura), the ambiens muscle being present in the former and absent in the latter. There are also other anatomical differences between them. The genus Conurus, therefore, as at pre- |