14 Jeffriks o;/ ///(? Sesajnoid of the Carpus in Birds. 



the sesamoid ossicle at the distal end of the radius in the Marsh 

 Hawk ( Circ7is hudsonius) as a new bone. Dr. Shufeldt says : 

 "• 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 figui'ed, 

 as it occurs in 'Aquila fucsa^ by Milne-Edwards in his famous 

 work on the Fossil Birds of France, the publication of which 

 beo"an in 1866, so that the bone as it occurs in the Falcojiidce can 

 scarcely be considered unknown to anatomists. The "os promi- 

 nens " as it occurs in the FalconidcB 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 \ 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 tne 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 ott'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 bone is described in Mivart's " Lessons in Elementary Anatomy," p. 320, fig. 

 289 ; and by Alix in liis " Essai sur I'Appareil locomoteur des Oiseaux," p. 403. Being 

 out of town fuller references cannot be given. 



t In his " Essai sur I'Appareil locomoteur des Oisseaux," Alix figures (pi. 11. fig. 

 12) the carpus of a Kestrel with a simple sesamoid. 



