Sept., 1894. THE BIRD'S FOOT. 209 



condition, the deep flexors being independent of one another, while 

 III, 2, and IV, 3, are, as in Ch.^tuva, forks of a common tendon, 

 separate tendons running to I, i, and II, i. Finally, in a number 

 of passerine birds we have, besides the separate deep flexors, the 

 following tendons, II, i, II, 2, III, i, III, 2, and IV, i, seven long 

 tendons in all. Concomitant with this there are other steps towards 

 increase in what we may call tendinal individuality, for while in the 

 Swifts the tendons playin a groove^ at the upper end of the tarso- 

 metatarsus, in some, though not in all, Passeres, there are six distinct 

 foramina for the accommodation of the seven tendons. 



Now the bearing of these facts on the case under consideration 

 seems to me this : There is an increase in the number and freedom 

 of tendons as we proceed from the lower to the higher birds, and if 

 three-toed birds retain the flexor longus hallucis it is because they 

 stand low in the avian scale and had lost their fourth toe before its 

 tendon became differentiated from the others. 



Right here is a point I should like to see explained. Why has 

 Channa — and Palamedea also — a thumb and no flexor ? Has it lost the 

 flexor through disuse, or has it, which it has no right to do, grown 

 a thumb after having once discarded that digit ? 



Turning back to Mr. Finn's interesting paper in the June 

 number, there are one or two points which invite a few additional 

 words. The great objection to Darwin's remark that " it might be 

 of advantage to a penguin-like bird first to flap along the surface of 

 the water like the Loggerhead Duck (Micropterns) and ultimately rise 

 in the air " is that, so far as I am aware, birds which take to water 

 have their flight impaired, and that the transition is from air to water, 

 and not from water to air. The Loggerhead Duck is said to fly when 

 young and do its flopping later in life. The auks have had their 

 wings much reduced in order to use them in a medium for which 

 they were not originally intended, while the great auk lost his power 

 of flight, and eventually his life, by not taking sufficient aerial 

 exercise. 



Lastly, is the foot with all toes turned forward a case of reversion 

 for adaptive purposes, or is it a case of survival ? While the suppo- 

 sition that, if birds are descended from reptiles, these reptiles were 

 arboreal in their habits seems to the writer as very plausible, it is also 

 fair to assume that there was a time when all four toes pointed for- 

 ward, 3 and why may not the cosmopolitan Swifts have retained their 

 toes as they were originally ? Opposed to this, however, is the highly 

 modified condition of the phalanges, and the fact that in Micropus the 

 tendons are a little more specialised than in Cha-tiira, which has the 



"^ Macyoptevyx has a single tendinal foramen, but the members of the genus 

 Macropteryx, though Swifts, belong, to the best of my knowledge and belief, to a 

 distinct family. 



•^ In support of this assumption is the fact that in the embryo the four toes 

 point forward. 



