Pico-Passerine Group of Birds. 31 



the hind plantar (or nearly so) ; but where the hallux is 

 much used (as in the Herons) the vinculum becomes very 

 small, and disappears altogether in the Bittern and in most 

 of the Passeres. The Passerine arrangement of the plantars 

 thus intergrades with the Galline arrangement, of which 

 it may be regarded as a modification. Two other slight 

 modifications of this arrangement appear in some of the 

 Falconidee. 



In comparison with the Galline arrangement of the plan- 

 tars and its modifications, the Picine arrangement appears to 

 be quite distinct. It only occurs in zygodactyle birds, but 

 not in all of them. In the typical Picine arrangement the 

 front plantar leads to the outer front (or 3rd) toe only, the 

 hind plantar dividing into three, to lead to the two hind 

 (the 1st and 4th) and the inner front (or 2nd) toes. A 

 slightly modified form of this arrangement occurs in the 

 Trogonidae, where the front plantar leads to the two front 

 toes (the 3rd and 4th), and the hind plantar to the two hind 

 toes (the 1st and 2nd). In the Picine arrangement, whether 

 typical or Trogonine, the front plantar does not lead to the 

 second toe. 



There remains yet a third arrangement of the deep plantar 

 tendons, which differs from either of the other two, or from 

 any of their modifications, to such an extent that it seems 

 to denote, in the birds which possess it, that it has been 

 derived by inheritance from a common ancestor, and has not 

 been independently acquired by any of them. It also 

 appears in two slightly differing forms, which have been 

 unitedly called synpelmous. In synpelmous birds the plan- 

 tars do not cross each other at the back of the tarsus (as in 

 all other birds), but coalesce at the point where they usually 

 cross. The peculiarity of this arrangement consists in the 

 remarkable fact that the hallux is contracted by a tendon 

 from the front plantar (instead of the hind plantar, as in all 

 other birds), sent down, in the Caprimulgidse and their 

 allies after, and in the Alcedinse and their allies before, its 

 coalescence with the hind plantar, the coalesced plantars 

 splitting into three to contract the three front toes. In the 



