190 ELEMENTS OF ORNITHOLOGY. 
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 furculwn 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 scme Parrots and 
Owls. 
The fureulum may anchylose with the manubrium of the 
sternum below and with the coracoid element above, as in Opis- 
thocomus, 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 epicleidiwm. Hach halt 
may be also expanded (as in the Fowl), where the two meet 
together in the middle line, and this latter expansion is termed 
the hypocleidium. 
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 
humero-scapulare, is generally present at the outer side of the 
shoulder-joint. 
The skeleton of the wing 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, 
