19© ELEMENTS OE OENITHOLOGY. 



The clavicle of each side usually anchyloses below with its 

 fellow of the opposite side to form a single more or less V-shaped 

 bone called the furcuhim or " merrythought." It is the least 

 constant of all the elements of the shoulder skeleton. It may 

 be entirely absent, as in the Apteryx and some Parrots ; or it 

 may be medially divided, as in the Emeu and some Parrots and 

 Owls. 



The furculum may anchylose with the manubrium of the 

 sternum below and with the coracoid element above, as in Opis- 

 tliocomus, and in some birds it anchyloses to the keel of the 

 sternum and also at the shoulder. 



Usually each half is expanded where it joins the coracoid and 

 scapula, and such expansion is called the epiclddium. Each half 

 may be also expanded (as in the Fowl), where the two meet 

 together in the middle line, and this latter expansion is termed 

 the Jiypocleidium. 



The clavicles, or two halves of the furculum, are generally 

 curved in two directions — convex outwards and convex forwards. 

 They serve to keep the shoulders apart — keeping the coracoids 

 apart during the downstroke of the wings — and their strength 

 and firmness are in direct relation with the powers of flight or 

 equivalent action in water. Thus they are very large in the 

 Penguin and immensely powerful. 



Where the clavicle, coracoid, and scapula meet together they 

 leave between them a foramen which, as we shall see, has an 

 important relation to the muscles of flight *. 



A very small bone or ossicle, called the scapula accessoria or 

 Jiumero-scapulare, is generally present at the outer side of the 

 shoulder-joint. 



The skeleton of the loing consists of a single bone, called the 

 " humerus," in the upper arm ; of two bones, named respectively 

 the " radius " and the " ulna," in the lower arm, and of the bones 

 of the pinion. These last-named bones answer to the bones of 

 our wrist, the middle part of our hand, and some of those of 

 our thumb and fingers. 



The humerus, or bone of the upper arm, is always a more or 

 less elongated and cylindrical bone, expanded at either end, but 

 especially at its upper, or proximal, end. This " upper end " or 

 head is transversely oblong, with a strongly marked ridge or 

 crest on its anterior, or ventral, surface. It articulates with the 

 glenoid surface of the shoulder-girdle. An orifice, which admits 

 * See below, p. 203. 



