| OCR Text |
Show 1876.] Of PASSERINE BIRDS. 509 the main muscle near the upper part of its inserted extremity. The comparatively insignificant triangular or compound fleshy belly thus formed, with its apex directed towards the elbow, terminates in a cylindrical tendon, which, included between the layers of the fibro-cutaneous patagium, takes a straight course to its insertion into the axially-running tendon of origin of the extensor metacarpi radialis longus of Schdpss, at a short distance from the tubercle on the humerus whence the muscle springs. As a result of this disposition, when the forearm is half-flexed, the tendon of the tensor patagii brevis is seen to enter the substance of the fibrous origin of the extensor met. rod. longus, and at right angles. This arrangement is indicated in Plate XLVIII. fig. 1, and is characteristic of the Picariee, as defined by myself to include the three subfamilies above referred to and them only *. Among the Passeres a slight, but easily recognizable, difference in the manner of insertion of the muscle maintains. The similarly single cylindroid tendon runs from the muscular belly, which has its origin at the shoulder, as above described, to the upper margin of the extensor met. rad. longus muscle, at an exactly similar spot: it does not, however, simply blend with the fibrous origin of that muscle; it becomes attached to it at the spot indicated, aud then (again considering the forearm as half bent upon the humerus) runs back inde.pendentlg to be attached to the base of the tubercle of origin of the extensor met. rad. longus, slightly below that muscle's springing-point. As a consequence of this arrangement there are two tendons to be seen running to one spot (that on the upper margin of the extensor met. rad. longus, where the tendon of the tensor meets it) from two points, one the apex of the tubercle on the humerus above referred to, and the other, the depression at its base. These tendons therefore converge as they leave the elbow, having at first an appreciable interval between them, which is gradually diminished as they approach, although they remain quite free from one another, that of the tensor being superficial. A glauce at Plate XLVIII. fig. 2, will serve to make this more clear. I have had the opportunity of looking at this muscle in nearly 150 species of Passerine birds, belonging to nearly all the most important sections. I first observed it in Pitangus sulphuratus, and shortly afterwards recognized the same arrangement in Hirundo urbica. A Humming-bird (Patagona gigas) and a Swift (Cypselus apus) coming to hand at about the same time (the former through the kindness of Professor Newton) impressed me with the distinction between the Macrochires and the Swallows, as far as these elbow-muscles are concerned. Thus stimulated by the significance of the character, I have since taken every opportunity at m y disposal to test its importance, the result being very favourable. Among the more aberrant genera I have examined are * P. Z. S. 1874, p. 123. PROC. ZOOL. Soc -1876, No. XXXIV. 34 |
