fy 
ON THE ANATOMY OF PASSERINE BIRDS. 357 
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 atiached to it at the spot indicated, and then (again consider- 
ing 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 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 appreci- 
able 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 [21] 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 
urbica. A humming-bird (Patagona gigas) and a Swift (Cypselus 
_ @pus) 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 disposal to 
test its importance, the result being very favourable. Among the 
more aberrant genera I have examined are 
_ Struthidea, Pitta, Cotinga, 
Heteralocha, Rupicola, Furnarius, 
Dicrurus, Lipaugus, Picolaptes, 
Prosthemadera, Tyrannus, Thamnophilus, 
Melanocorypha, _ Chasmoryhynchus, Grallaria, 
Strepera, Pipra, Pteroptochus, 
_ Menura, Tityra, Hylactes. 
Atrichia, Hadrostomus, 
The only apparent exceptions I have found are the following. 
In Pteroptochus albicollis and in Hylactes megapodius the muscular 
fibres of the extensor met. rad. longus almost surround and enclose 
the tendons in question. Such being the case, the arrangement does 
not at first sight appear typically Passerine. Nevertheless, upon 
removing or pushing to one side these covering fibres, the two tendons 
are seen arranged exactly asin other members of the Order. 
