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Show 1883.] APPARATUS OF THE TENUIROSTRES. 63 for comparison ; they afford an illustration of the fact that similar functional requirements frequently lead to the development of similar structures in animals which are otherwise very distinct. The skeletal framework of the hyoid apparatus does not present any important peculiarities. It consists:-(1) of the two posterior or long cornua, which are extremely long in the Trochilidae, but very short in Zosterops and Certhia, whilst in the Meliphagidse and in the Nectariniina their apices do not reach further than the frontal bones ; (2) the basihyal, unpaired and formed by a slender bony rod, bifurcating at each end; (3) the os entoglossum, which is paired, the two parts articulating with the anterior ends of the basihyal, and ending as fine, tapering, more or less cartilaginous rods ; (4) a urohyal, attached to the ventral aspect of the trachea by a short ligament, its anterior portion articulating with the basihyal. This little bone does not serve for the origin or the insertion of any muscles in the birds in question. The anterior or short cornua have become obsolete. In the Trochilida? the basihyal is extremely thin and short, whilst the urohyal seems to be generally absent, and the long cornua and the entoglossal bones are very long. The horny sheath surrounding the os or ossa entoglossa, and projecting more or less in front of them, exhibits very great differences in the various groups of Tenuirostral birds. The simplest form is represented by Zosterops (Plate XVI. fig. 2). The tongue ends in two short filaments, whilst the greater portion of the tongue proper is not divided; dorsal and ventral aspect smooth, hinder portion of horny sheath projecting backwards with a few (about 3-4) horny spines. In Certhia the tongue corresponds with the length of the bill; its lateral margins are transformed into sharp cutting-edges ; the tip is frequently split into three short bristles of irregular shape; the posterior margin ends much as in Zosterops. Along the middle line on the upper surface of the tongue we notice a slight depression. Whilst in the two genera described above the horny sheath of the tongue shows still a very simple formation; it has in the following families been developed into a very complicated and elaborate organ. In order to ascertain the formation of the tubular tongues of the Nectariniina and Meliphagina, I have made a series of transverse sections through that organ in Nectarinia splendida, Cinnyris auri-ceps, Anthothreptes malaccensis, A. subcollaris, Prosthemadera, Ptilotis carunculata, and, for comparison, of a species of tbe Trochilida?. The accompanying drawing (fig. 1, p. 64) represents a series of eight stages of the tongue of Cinnyris, whilst figures 8 and 10 of Plate XVI. show the entire tubes as seen from the ventral side. Near the root of the tongue, i. e. near tbe basal part of the os entoglossum, the dorsal and ventral halves of the horny sheath with which the tongue is covered project to the right and left sides, so as to form sharp, more or less cutting-edges. A little more in front, hese lateral parts are slightly curved upwards, the ventral sheath |
