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SKELETON 





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Ms. 



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Mt.III 



The Toes are generally four in number, and no trace of a fifth 

 lias been or is likely to be discovered, considering the extreme 

 reduction and ephemeral occurrence of the fifth metatarsal element. 

 The number of i^halanges 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 tyjiical plan in the pentadadyl Bird, 



which omitatis mutandis 

 may be made equally ap- 

 plicable to the Bird's 

 "hand." There are first 

 three proximal tarsals 

 M'hich fuse with each 

 other and then Math the 

 distal end of the tibia, 

 while that of the fibula 

 withdraws from direct 

 contact with the outer or 

 fibular tarsal. The united 

 mass of these then sends 

 out an ascending process 

 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, whereupon 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 3rd, and fuse together from above 

 downwards. The 5th or outer metatarsal element has only been observed 

 in earlj' embryos, soon disappearing by resorbtion, and the same may be 

 said of its distal tarsal. The 1st metatarsal remains sej^arate 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, 3rd 

 and 4th, but loses its jiroximal position and thereliy 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 Steganojyodes. 



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 Hatitm and Crypturi, 

 developing into a separate bone which is wedged in from behind between the 

 tibio-tarsal and tarso-metatarsal surfaces. Tliis bone was described many years 

 ago by Owen either as a calcaneus or calcaneal sesamoid, but now properly by 

 Gegenbaur {Uivtersuchungen zur vergleichcnden Anatomic, i. p. 104) and Morse 

 {Ann. Lye. Nat. Hist. New York, x. p. 141) as the central tarsal, the latter figur- 

 ing it as found in Tyrannus. Sir Walter BuUer {B. N. Zeal. ed. 2. ii. pp. 333, 

 334, pi. xlix.) was unfortunately induced to figure and describe it in Dinornis as 

 " an astragalus-like bone." 



