1888. ] NEW YORK ACADEMY OF SCIENCES. 93 
phalanges, is situated near the carpus, is easily flexible laterally 
as well as in the plane of the wing, and forms what is known 
as the alula or bastard wing. It covers the base of the outer 
primaries and has no important function. The second digit, 
corresponding to the middle finger in man, consists of two 
phalanges, and forms, by its size and length, the main bone*of 
the digital portion of the hand. The third, corresponding to 
the ring finger in man, consists of a slight spur of bone seated 
on the inner edge of the metacarpal bone. ‘The pinion, or 
manus, which is the part of the wing to which the primaries 
are attached, thus consists of three segments: first, the meta- 
carpals, forming rather more than one-half its length ; second, 
the first phalange of digit il1.; third, the second phalange of 
digit i1i., this latter forming the tip of wing. Practically, then, 
the pinion is made up of two slender partly anchylosed meta- 
carpal bones lying side by side, and surmounted by one long 
finger composed of two segments. This gives two joints sus- 
ceptible of slight motion, strictly in the plane of the wing, 
the outer alone allowing a very slight lateral deflection. 
There is no possibility of any rotation at either of these joints, 
so long as the ligaments binding them together are not lace- 
rated. A slight loosening of the ligaments will give the ap- 
parently wide range of motion shown in the preparations ex- 
hibited at the meeting of December 19th. The slight motion 
furnished by the two joints in the hand facilitate the close 
shutting of the primaries when the wing is folded, and their 
complete extension in flight. 
The muscles which enter into the mechanism of flight are 
numerous and complicated. The large muscles, seated upon 
the sternum, which act upon the humerus and elevate and de- 
press the whole wing in flight, need not be considered in this con- 
nection. ‘The muscles of the wing proper are about twenty-five 
in number, and will be briefly reviewed. They may be divided 
into three sets; first, those of the upper arm; second, those of 
the forearm; third, those of the hand. ‘Those of the upper 
arm having no special bearing on the present discussion may be 
passed over without further notice. The muscles of the fore- 
arm are ten in number, as follows: 
1. Flexor carpi ulnaris, having its origin at the internal 
condyle of the humerus, and its insertion on the ulna at the 
wrist. Its important function is to keep the cubitus and meta- 
carpus firm at any desired angle, besides preventing a too 
strong extension of the metacarpus. 
2. Musculus ulni-metacarpalis ventralis.—Originates on the 
ulna, and is inserted on the second metacarpal. Aids the 
preceding muscle, and tends to draw the metacarpus down. 
