864 



SKELETON 



mentioned is a deep cavity crossed by a transverse bridge, acting as 

 a pulley for the tendon of the mii&c. extensor digitorum communis 

 (page 612) which passes beneath it. In the majority of Birds 

 this bridge is ossified, as in Dinornithes (page 579), Phmwhacos, 

 Gastornis (page 281) and the other Garinatie not named below, but 

 it remains tendinous or cartilaginous, and is thus often described 

 as non-existent, in a good many, as Struthio, Rhea, Dromieus, Casuarms, 

 JE'pyornis, Brontornis, Opistliocomm, Striges, Todus, Buceros, Capimulgi 

 and Trochili ; while it varies, being either soft or osseous, in AjHeryx, 

 Podicipes and Psittaci. The Fibula articulates by its head with the 

 outer condyle of the Femur, leaning also on the lateral knob on the 

 head of the Tibia, and lower down is connected with the peroneal 

 ridge by a rough surface. The distal end of the Fibula is always 

 much reduced and fuses more or less completely with the outer 

 side of the tibio-tai'sus, generally ending in a sharp point.^ 



The Metatarsus, or ^^ Tarsus" as it is commonly but incorrectly called 

 by ornithologists, is a compound structure made up of the second, 



I.a.c. 



\0.a.c. 



VI. I. 



-in.e. 



Pavo. Tibia and Tarso-metatarsus, 

 front view. 



F. Fibula ; I.a.c. aud O.a.c. inner and 

 outer anterior crest ; m.i. m.e. 

 inner and outer malleolus ; Sp. 

 exostosis, carrying spur; T.a. in- 

 sertion of Tibialis anticus. 



r.A. 



Cygnus. 



Pavo. 



Proximal end of left 

 Tarso-metatarsus, back 

 view. — F.jh groove and 

 canal for m. flexor pro- 

 fundus; P.}). groove for 

 deep peroneal ; T.A. 

 ridge for tendo Acliilli.s. 



^ Dr. Sliufeldt {3is, 1894, p. 361) takes exception to the statement previously 

 made in this volume (page 249) describing and partly figuring some cases, that 

 appear to me exceptional if not abnormal, in which the Fibula is "complete 

 and reaches the tarsal epiphysis of the tibio-tarsus. " But my statement appears 

 to have been misunderstood, and I may repeat that the ankle-joint "is never 

 normally reached " by the Fibula, nor, for the matter of that, by the Tibia 

 either. A complete account of these features was published in 1891 (Thier- 

 7'eich, Vogel, pp. 980, 981), wherein also exceptional occurrences of a complete 

 Fibula in Birds are mentioned. 



