V. 
NOTE ON SIR BALDWIN SPENCER’S DISSECTION OF 
THE WING OF THE STEAMER DUCK —TACHTERES 
CINEREUS (Gm.) 
By B. W. TUCKER 
T HE Loggerhead or Steamer Duck— Tachy eres cinereus (Gm.) has 
long been familiar to voyagers in the Straits of Magellan and the 
neighbouring waters on account of its habit (referred to in Sir Baldwin 
Spencer’s notes, p. 80) of paddling with its wings along the surface 
of the water instead of flying. Completely flightless individuals and 
others capable of flight both occur, but whether these represent two 
distinct species or whether the flying birds are immature individuals, 
which lose the power of flight as they grow older and heavier, is not 
even now quite certain, though the balance of probability seems to 
favour the latter view (see, for example, R. O. Cunningham, Trans. 
Zool. Soc ., vii, 1871, pp. 493—501). 
Sir Baldwin Spencer’s dissection was made on an adult flightless 
bird, evidently in the expectation of finding some aberrant features of 
the musculature correlated with the peculiar habit above mentioned. 
Unfortunately the diagrams do not provide a complete picture of the 
musculature of the wing. Neither the muscles of the external aspect of 
the forearm nor any of the intrinsic muscles of the hand are illustrated, 
and in the absence of any detailed notes on the dissection some other 
points in the anatomy are left in doubt. The diagrams, however, as 
far as they go, reveal hardly any notable difference from the common 
Mallard— Anas platyrhyncha L. (= boscas L.) Although the wings 
are small and useless for flight, the wing musculature, particularly that 
of the forearm, evidently remains very strongly developed in connexion 
with the paddling habit, and appears to have undergone no striking 
modification as a result of the change of function. Some modification 
in the region of the shoulder-joint might perhaps be anticipated, but if 
any exists the dissection of this region has not been carried far enough 
to reveal it. The division of the biceps corresponding to its two in¬ 
sertions on the radius and ulna respectively appears to be carried well 
up into the belly of the muscle, certainly much farther than in Anas, 
though I have not had an opportunity of examining any diving duck 
