1 4 Jeffries on the Sesamoid of the Carpus in Birds. 
the sesamoid ossicle at the distal end of the radius in the Marsh 
Hawk ( Circus hudsonius ) as a new bone. Dr. Shufeldt says : 
u It does not seem possible that a bone the size of one which I am 
now about to describe could have been entirely overlooked by 
ornithologists, yet after a careful perusal of such parts of the 
works of the most prominent writers, as refer to the skeletology 
of the upper extremity I fail to discover the barest mention as 
to the existence of any such an one.” Now this bone was figured, 
as it occurs in Aquila ficsa , by Milne-Edwards in his famous 
work on the Fossil Birds of France, the publication of which 
began in 1866, so that the bone as it occurs in the Falconidce can 
scarcely be considered unknown to anatomists. The u os promi- 
nens” as it occurs in the Falconidce is a modification of the ses- 
amoid ossicle which very often occurs in the tendon of the tensor 
petagii longus where it passes over the carpus ;* its function here 
being that of a simple sesamoid over the carpus. In many of 
the Falconidce f this sesamoid becomes bound to the distal end 
of the radius, and lengthened out at right angles to the long axis 
of that bone, as figured by Dr. Shufeldt. By this means tiie func- 
tion of the ossicle becomes very much altered. It no longer 
slides over the carpus, but serves, since the tendon of the extensor 
petagii longus includes only its free end, to 'keep that tendon off the 
carpus, thus avoiding friction at the joint. Again, since the ossicle 
attains considerable length, — 6 centimeters (millimeters?) ac- 
cording to Dr. Shufeldt in Circus , — it materially alters the 
action of the extensor petagii longus so that it tends much more 
to extend the hand and draw the thumb away from the index. In 
this way the extensor petagii longus seems to antagonize the slip 
of the flexor longus digitorum sublimis, and since its tendon is 
elastic, owing to the amount of yellow fibrous tissue in it, the 
action must be to a considerable degree automatic. 
My views of the functions of this ossicle are, it will be seen, 
very different from those of Dr. Shufeldt, who considers it to 
protect the carpus and greatly increase the area of the wing. 
This bone, standing up as it does on the anterior edge of the 
* This bonq is described in Mivart’s “ Lessons in Elementary Anatomy,” p. 320, fig. 
289 ; and by Alix in his “ Essai sur l’Appareil locomoteur des Oiseaux,” p. 403. Being 
out of town fuller references cannot be given. 
t In his “ Essai sur FAppareil locomoteur des Oisseaux," Alix figures (pi. 11. fig. 
12) the carpus of a Kestrel with a simple sesamoid. 
