THE FOOT IN BIEDS. 



297 



Fitr. 89. 



Frigate-bird (Phaethon) and in Steatornis, the haJhical 

 metatarsal is remarkably long. Tlie genus Phaethon stands 

 alone, so far as I know, in having the 

 hallucal metatarsal ankylosed with 

 the others. 



In many of the Alectoromorphce, a 

 spur (calcar), consisting of a bony 

 core ensheathed in horn, is developed 

 on the inner side of the metatarsus, 

 and becomes ankylosed with the me- 

 tatarsal of the second digit. In a few 

 birds, similar spurs (Palamedea), or 

 osseous excrescences {Pezopha-ps), are 

 developed in relation with the meta- 

 carpus. 



The normal number of the pedal 

 phalanges in birds is (as in ordinaiy 

 Lacertilia) 2, 3, 4, 5, reckoning from 

 the hallux to the fourth digit. Among 

 the few birds which constitute excep- 

 tions to the rule are the Swifts, in 

 which the third and foiu'th toe have 

 only three phalanges each (2, 3, 3, 3), 

 and the Goatsuckers and the Sand- 

 grovise, in which the foxu'th toe only 

 has the number thus reduced (2, 3, 4,3). 



Many birds have only three toes, by suppression of the 

 hallux. In the Ostrich, not only the hallux, but the pha- 

 langes of the second digit, are suppressed ; and the distal 

 end of the second metatarsal is reduced to a mere rudiment. 

 Hence the ostrich has only two toes (which answer to the 

 third and fourth of the pentadactyle foot), with four pha- 

 langes in the inner and five in the oufcei", though the inner 

 toe is far the longer and the stronger. 



In most four-toed birds the halliix is turned more or less 

 completely backwards, and the other three digits forwards. 

 But in many Aetomorphce (especially the Owls), the outer toe 

 can be turned outwards, or even backwards, at will. And in 



Fig. 83. — The right 

 tarso-metatarsus of a 

 Fowl, consisting of 

 three digits, ii., iii., 

 iv., ankylosed with 

 one another, and with 

 the osseous core of 

 the spur. A., front 

 aspect; B., inner as- 

 pect. 



