THE ANATOMY OF BIRDS. — OSTEOLOGY 



147 



The Clavicles, or Furculum (Lat. clavieula, a little key : fu/rculunij a little fork ; 

 figs. 56, 59, cI), or the clavicular arch, are the pair of bones which when united together form 

 the object well known as the " merry-thought" or ** wish-bone," corresponding to the human 

 " collar-bones." They lie in front of tlie breast, across the middle line of the body like a A' 

 or U ; the upper ends uniting as a rule both with scapula and coracoid. For this purpose, in 

 most birds, the ends are expanded more or less ; such expansion is called the epicleidium (Gi'. 

 fTTt, epi, upon ; icKfiSiov, Tdeidion, the collar-bone) ; in Passerine birds it is said to ossify separ- 

 ately, and is considered by Parker to i-epresent the proeoraeoid of reptiles. At the point of 

 union below, the bones often develop a process (well shown in the domestic fowl) called the hypo- 

 cleidium (Gr. vno, hypo, under; fig. 59, he), supposed to represent the interclavicle of reptiles. 

 The clavicles are as a rule present, perfect, anchylosed together, articulated at the shoulder; in a 

 few birds anchylosed there; in several, there and 

 with the keel of the sternum ; in Opisthocomus there 

 and ^vith the manubrium of the sternum. In various 

 birds, chiefly Picarian and Psittaciue, they are de- 

 fective, not meeting each other. They are wanting 

 in Sti'uthio, Bhea, Apteryx, and some Psittacidce. 

 Besides curving toward each other, the clavicles 

 have usually a fore-and-aft curvature, convex for- 

 ward. In general, the strength of the clavicles, 

 the firmness of their connections, and the openness 

 of the V or U, are indications of the volitorial or 

 natatorial power of the wings. The end of the fur- 

 ealum is hollowed for a fold of the windpipe in the 

 crested pintado (Owen). 



4. THE PELVIC ARCH. 



The Pelvis (Lat. pelvis, a basin, fig. 60), is 

 that posterior part of the trunk which receives the 

 uro-genital, and lower portion of the digestive, vis- 

 cera. It consists of the "sacral" vertebrae on the 

 middle dorsal line, flanked on each side by the bones 

 of the pelvic arch, which supports the hind limb. 

 In vertebrates generally the pelvic basin is com- 

 pleted on the ventral aspect by union (symphysis ; 

 Gr. (Tvv, sun, together ; (^ivais, grox^nh) of the bones 

 from opposite sides. Excepting only Struthio, which 

 has a pubic symphysis ; and Bhea, which has an 

 ischiac symphysis just below the sacral vertebrae, 

 the pelvis of a bird is entirely open below and 

 behind; each pelvic arch anchylosing firmly with 

 the sacral vertebrae to form a roof over the viscera 

 above named. This sacro-iliac anchylosis is com- 

 monly coextensive with the confluence of the many 

 vertebrae which make the "sacrum" of ordinary 

 language, that is, ft-om the first dorso-lumbar to the 

 last uro-sacral. The whole roof-like affair looks 

 something like a keelless sternum inverted. The 

 pelvic arch of each side consists of three bones, ilium, 



Fig. 60. — Pelvis of a heron (Ardea herodias), 

 nat. size, viewed from below; from nature by Dr. 

 R. W. Shufeldt, U.S.A. dl, dorso-lumbar vertebra 

 to and including the last one, sc ; below sc, for the 

 extent of the lart/i' black spaces ( opposite the arrow ) 

 are the true sacral vertebrte ; its, urosacral verte- 

 brse (opposite the five oval black spaces ; II, ilium ; 

 Is, ischium; P, pubis; oh, obturator foramen. 

 The arrow flies into the acetabulum. 



