‘92 TRANSACTIONS OF THE [JAN. 9, 
further surface for the attachment of the pectoral muscles. They 
are very broad at the sternal end, where they have the character 
of a strongly buttressed pillar, preventing lateral motion of the 
shoulder. The clavicles, attached distally to the shoulders, unite 
in front, forming an arch, which is bound by ligaments to the 
keel of the sternum, thus bracing the shoulders laterally, and pre- 
venting them from approaching each other. The long thin sca- 
pula, running upward and backward from the shoulder joint, and 
firmly bound to the thorax by strong muscles, gives stability to 
the shoulder in an upward direction. The shoulder joint itself 
is formed by the junction of the scapule, coracoids, and clav- 
icles, where they are either anchylosed or bound firmly together 
by ligaments, giving a firm support for the head of the humerus, 
from which the motion of the wing proceeds. The humerus, as 
already said, has great freedom of movement at the shoulder; 
distally, at the elbow joint, it meets the two bones of the fore- 
arm, with which it articulates by a hinge joint, admitting of 
motion in but one direction, namely, in the plane of the ex- 
tended wing. Any rotation is prevented by the character of the 
joint itself, and a special set of short muscles in addition to the 
ligaments usually present to give firmness to the joint. 
The bones of the forearm have no rotatory motion whatever, 
but an antero-posterior movement upon themselves, alluded to 
during the evening of December 12th, as a brilliant but long- 
overlooked discovery of the late Professor Wyman. I then felt 
called upon to state that it was a contrivance so well known as 
to be specially dwelt upon in ornithological text-books as one of 
the most distinctive and striking features of a bird’s wing, and 
as such familiar to every well-informed ornithologist. As Dr. 
Coues has since shown in a recent letter in Science, it was dis- 
covered nearly twenty years before it was made known by Wyman, 
and has had, during the last fifty years, no less than four indepen- 
dent discoverers. ‘This mechanism is so important, interesting, 
and beautiful, that I have brought here a preparation which 
shows it, and which I shall exhibit later. 
At the wrist-joint, motion is possible only in the direction of 
the plane of the expanded wing, the hand being incapable of 
rotating at the wrist, the joint being strictly a hinge joint. 
Two small bones compose the carpus, which participate in and 
render possible the sliding movement of the bones of the fore- 
arm. ‘The hand consists of a compound metacarpal bone, 
which is really made up of three anchylosed metacarpals, to 
which are attached three digits, corresponding to digits il., ili., 
and iv., of the human hand, the first and fifth digits being ab- 
sent in birds. ‘The first digit in birds is usually called thumb, 
though really homologous with the index finger. It has two 
