49O MANUAL OF ZOOLOGY. 



of the three toes which are directed forwards, consists of three 

 phalanges; the next has four phalanges ; and the outermost toe 

 is made up sifive phalanges (fig. 214, A). This increase in an 

 arithmetical ratio of the phalanges of the toes, in proceeding 

 from the inner to the outer side of the foot, obtains in almost 

 all birds, and enables us readily to detect which digit is sup- 

 pressed, when the normal four are not all present. Variations 

 of different kinds exist, however, in the number and disposi- 



P 



Fig. 214. A, Hind-limb of the Loon (Colymbus glacialis) after Owen ; i Innominate 

 bone ; f Thigh-bone or femur ; t Tibia, with the proximal portion of the tarsus an- 

 chylosed to its lower end ; r Fibula ; m Tarso-metatarsus, consisting of the distal 

 portion of the tarsus anchylosed with the metatarsus ; pp Phalanges of the toes ; B, 

 Tail of the Golden Eagle ; s Ploughshare-bone, carrying the great tail-feathers. 



tion of the toes. In many birds such as the Parrots the 

 outermost toe is turned backwards, so that there are two toes 

 in front and two behind. In others, again, the outer toe is 

 normally directed forwards, but can be turned backwards at 

 the will of the animal. In the Swifts, on the other hand, all 

 four toes are present, but they are all turned forwards. In 

 many cases especially amongst the Natatorial birds the 



