866 SKELETON 
The Toes are generally four in number, and no trace of a fifth 
has been or is likely to be discovered, considering the extreme 
reduction and ephemeral occurrence of the fifth metatarsal element. 
The number of phalanges typically increases in arithmetical series 
from 2 on the first or HALLUX (pages 404, 405) to 5 on the fourth 
by a short sketch of their development, and its comprehension may be assisted 
by the accompanying diagram shewing the typical plan in the pentadactyl Bird, 
which mutatis mutandis 
may be made equally ap- 
i vs ." Zr, plicable to the Bird’s 
; “‘hand.” There are first 
t f I three proximal  tarsals 
Rk es (ihe On (6 which fuse with each 
or Oey 45 %@ other and then with the 
Vi oa distal end of the tibia, 
Yy Ws | Mtg while that of the fibula 
O | Za withdraws from direct 
? 
A i] [] \\ \y i \\ Mt LIT contact with the outer or 
fibular tarsal. The united 
\ mass of these then sends 
q out an ascending process 
q which fuses with the front 
of the tibial intercon- 
dylar furrow. At an early 
period the five distal tarsals fuse into one cartilaginous mass, in which only 
one centre of ossification appears, wheretipon it fuses with the upper end of 
the 2nd, 3rd and 4th metatarsals. These being originally separate, soon 
press backwards the upper end of the 8rd, and fuse together from above 
downwards. The 5th or outer metatarsal element has only been observed 
in early embryos, soon disappearing by resorbtion, and the same may be 
said of its distal tarsal. The 1st metatarsal remains separate on the inner side 
of the 2nd—a condition which persists in the Penguins; but in other 4- 
toed Birds it does not keep up with the lengthening growth of the 2nd, 8rd 
and 4th, but loses its proximal position and thereby its connexion with the 
tarsal region, lying in the majority of Birds along the inner hind margin of the 
lower end of the united ‘‘metatarsus,” retaining (or regaining) its position in 
their plane in Steganopodes. 
Besides the 3 proximal and 5 distal tarsals just mentioned, the diagram 
shews a ninth element—a central tarsal, which is sometimes double. Appearing 
in the embryo as distinct cartilaginous nodules, they are soon buried in the 
fibrous interarticular pad, and in the majority of birds ultimately vanish. 
However one of them occasionally persists, as in the Ratite and Crypturt, 
developing into a separate bone which is wedged in from behind between the 
tibio-tarsal and tarso-metatarsal surfaces. This bone was described many years 
ago by Owen either as a calcaneus or calcaneal sesamoid, but now properly by 
Gegenbaur (Untersuchungen zur vergleichenden Anatomie, i. p. 104) and Morse 
(Ann. Lyc. Nat. Hist. New York, x. p. 141) as the central tarsal, the latter figur- 
ing it as found in Tyrannus. Sir Walter Buller (BP. N. Zeal. ed. 2. ii. pp. 338, 
334, pl. xlix.) was unfortunately induced to figure and describe it in Dinornis as 
“‘an astragalus-like bone.” 
LV 
