1894- THE BIRD'S FOOT. 213 



communis. It is a rounder and narrower muscle, entirely distinct 

 from and unconnected with the flexor communis above the ankle- 

 joint, and arising by a single head or by two heads from the external 

 condyle of the femur, and from the intercondylar region. Its single 

 tendon of insertion passes through the ankle-joint, generally through 

 a separate bony canal which is placed more laterally than the 

 bony canal of the flexor communis. Below the ankle-joint the 

 tendons of the two muscles lie side by side, but m their course down 

 the shaft of the tarsus-metatarsus the tendon of the flexor hallucis 

 crosses over the tendon of the other, and in so doing (as has already 

 been mentioned) except in the Passeres and Humming-birds, it sends 

 a strong vinculum to the communis tendon, and then runs on to its 

 insertion in the hallux. Now whatever may have been their 

 original connection, these two muscles are as distinct and individual 

 as possible. In the case of an ordinary three-toed bird like the 

 Oyster-Catcher [HcBinatopus ostralegiis), the two muscles are as separate 

 in their origin and course as in a normal four-toed bird ; the only 

 difference is, that with the loss of the hallux, the slip of tendon 

 which runs from below the vinculum to the tendon has disappeared. 

 The facts almost irresistibly bear out the conclusion that such a 

 three-toed bird has been derived from a four-toed bird not of a 

 primitive character, but with a foot like existing normal four-toed 

 birds. But evidence — one is almost tempted to call it experimental 

 evidence — is furnished in favour of this view by the anatomy of 

 the foot of Pterocles. Whether the Sand-grouse be considered a 

 pigeon or a gallinaceous bird, most will agree that it is in the 

 present condition of losing its great toe. In Pterocles alchata there 

 is no trace whatever of the slip from the vinculum to the minute toe. 

 But above that the two tendons, and above the ankle-joint the two 

 muscles, are perfectly distinct ; the flexor longus hallucis arises by 

 two heads from the femur, while the flexor communis spreads out 

 over the upper end of the tibio-tarsal shaft. Here is a case of recent 

 degeneration of a hallux and the production of the same type of foot 

 as in ordinary three-toed birds. It seems to me absolutely conclusive 

 in favour of Mr. Finn's view. 



But Mr. Lucas's remark about Chauna and Palamedea calls up 

 another exceedingly strong piece of evidence. Chauna has no flexor 

 tendon to its hallux, but in other respects the relations of the flexor 

 longus hallucis down to the vinculum are precisely similar to those of 

 four-toed birds. Mr. Beddard and I recently had an opportunity of 

 dissecting Palamedea, and the results of our observations, communi- 

 cated to the Zoological Society, will shortly be published in its 

 Pyoceedings. We found that there was a separate tendinous slip to 

 the hallux. So here again is a case showing that the mere sup- 

 pression of the tendinous slip from the vinculum to the hallux 

 changes a four-toed foot into the type of structure found in three-toed 

 birds. 



