EXTERNAL FAKTS OF BIRDS. ~ THE FEET. 



131 



Fig. 48. — Semipal- 

 rnation in Ereunetes ; 

 iiat. size. 



Pig. 49. — Semi- 

 palmated bases of 

 toes of Si/mphf^mla; 

 nat. size. 



It is actually the 



exhibit the transition fruui the perching to the gradient foot, in some reduction of the hind toe, 

 which is nevertlieless in most cases still on the same level as the rest (tig. 38, b). lu the 

 gallinaceous or rasorial (Lat. rasor, a scraper) birds, which are essentially terrestrial, and 

 noted for their habit of scratching the ground for food, the hind toe is decidedly elevated and 

 shortened in almost all of the families (fig. 35). Such reduction and upUfting of the hallux is 

 carried to an extreme in most of the waders, or gral- 

 latores, in many of which this toe dis.ijipi'ars (figs. 

 38, a, 39). It is scarcely practicable to recognize special 

 modifications of such gradient or grallatorial feet, since 

 they merge insensibly into one another. The herons, 

 which are the most arboricole of the waders, exhibit a 

 reversion to the insessorial type, in the length and in- 

 cumbency of the hallux. The mode of union of the 

 front toes of the walkers and waders is somewhat char- 

 acteristic. The toes are either cleft quite to the base, 

 or there joined by small webs ; probably never actually coherent. Such 

 basal webbing of the toes is called semipalmation (" half- webbing "). 

 same thing that occurs in many birds of prey, in most gallinaceous birds, etc. ; the term is 

 mostly restricted, in descriptive ornithology, to those loading birds, or grallatores, in wliich it 

 occurs. Such basal webs generally run out to the end of the first, or along part of the second, 

 phalanx of the toes ; usually farther between the outer and middle 

 than between the middle and inner toes. Sucli a foot is well illus- 

 trated by the semipalmated plover {Mgialites semipahnatus), 

 semipalmated sandpiper (Ereunetes pusillus, fig. 48), and willet 

 {Symphemia semipalmata, fig. 49). In a few wading birds, as the 

 avocet and flamingo, tire webs extend to the ends of the toes. 

 This introduces us at once to the third main modification of the 

 foot, 3. TTie natatorial type. Hero the foot is transformed into 

 a swimming implement, usually with much if not entire abrogation 

 of its function as foot or hand. Swimming birds with few ex- 

 ceptions are notoriously bad walkers, and few of them are perchers. 

 The swimming type is presented under two principal modifica- 

 tii ms : — (a.) In the palmate or ordinary webbed foot, all the front piQ gQ, _ paimate foot of a 

 toes are united by ample webs (fig. 50). The palmation is usually tern, sterna forsteri; nat, size, 

 complete, extending to the ends of the toes ; but one or both webs may be so deeply incised, 

 that is, cut away, that the palmation is practically reduced to semipalmation, as in terns of 

 the genus HydrocheUdon (fig. 51). The totipalmate is a special case of palmation, in 

 which all four toes are webbed ; this characterizes the whole order 

 Steganopodes (fig. 52). (&.) In the lohate foot, a paddle results not 

 from connecting webs, but from a series of lohes or flaps along the 

 sides of the individual toes ; as in the coots, grebes, phalaropes, and 

 sun-birds (Heliornithidce) . Lobation is usually associated with semi- 

 palmation, as is well seen in the grebes (Podicipedida) . In the snipe- 

 like phalaropes (Phalaropodidce) , lobation is present as a modification 

 of a foot otherwise quite cursorial. The most emphatic cases of loba- 

 tion are those in which each joint of the toes has its own flap, with a 

 free convex border ; the membranes as a whole therefore present a scol- 

 loped outline (figs. 53, 53 bis). Such lobes are merely a development 

 of certain marginal fringes or processes exhibited by many non-lobate or non-palmate birds. 

 Thus, if the foot of some of the gallinules be examined in a fresh state, the toes will be seen to 



Fig. 51. — Incised pal- 

 mation of HydrocheUdon 

 lariformis ; nat. size. 



