1876.] OK 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 Schopss, 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. rad. longus, and at right 

 •angles. This arrangement is indicated in Plate XLVIII. fig. 1, and 

 is characteristic of the Picarise, 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, and then 

 (again considering the forearm as half bent upon the humerus) 

 runs back independently to be attached to the base of the tubercle 

 of origin of the extensor met. rad. longus, slightly below that 

 muscle's springiug-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 glance 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 im- 

 portant sections. I first observed it in Pitangus sulphuratus, and 

 shortly afterwards recognized the same arrangement in Hirundo 

 ttrbica. A Humming-bird (Patagona gigas) and a Swift (Cyp- 

 selus 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 my dis- 

 posal 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— 1870, No. XXXIV. 34 



