As a general observation, it may be stated, that the fork is strong and elastic, and its branches wide, arched, and car ried forwards upon the body, in propor tion as the bird possesses strength and rapidity of flight ; and accordingly the struthious birds (ostrich and cassowary,) which are incapable of this mode of pro gression, have the fork very imperfectly formed. The two branches are very short, and never united in the African ostrich, but are anchylosed with the scapula and clavicle. The cassowary has merely two little processes from the side of the clavicle, which are the rudiments of the branches of the fork. In the New Holland ostrich there are two very small thin bones, which are at tached to the anterior edge of the dor sal end of the clavicles by ligaments ; they are directed upwards towards the neck, where they are fastened to each other by means of a ligament, and have no connection whatever with the ster num.
The bones of the wing may be com pared, on the whole, to those of the tip per extremity in man ; and consist of an os humeri ; two bones of the fore-arm ; two of the carpus ; two, which are gene rally consolidated together, of the meta carpus ; one bone of the thumb, and two fingers.
The stork, and some others of the gral ix, which sleep standing on one foot, possess a curious mechanism for preserv ing the leg in a state of extension, with out any, or at least with little, muscular effort. There arises from the fore-part of the head of the metatarsal bone a round eminence, which passes up be. tween the projections of the pulley, on the anterior part of the end of the tibia. This eminence affords a sufficient degree of resistance to the flexion of the leg, to counteract the effect of the oscilla tions of the body, and would prove an insurmountable obstruction to the mu tien of the joint, if there were not a socket, within the upper part of the pulley of the tibia, to receive it when the leg is in the bent position. The lower edge of the socket is prominent and sharp, and presents a sort of barrier to the ad mission of the eminence, that requires a' voluntary muscular exertion of the bird to overcome, which being accomplished, it slips in with some force, like the end of a dislocated bone.