FEIGHT 261 
Before analyzing these modes of aerial locomotion, it is desirable 
to refer to some of the conditions under which birds are placed, since 
these must be taken into account if it be desired to understand the 
problems of flight. What, in the first place, is known about the 
relation between the weight of birds and the area of their wings, 
and how do birds differ from one another in this respect? This 
subject has been carefully studied by Miillenhoff+t and others. It 
has been found that the relation of the wing- or rather sail-area to 
the weight of the bird varies greatly. As might be expected, the 
greater the sail-area, the more powerful, other things being equal, 
is the flight. 
Another matter in which birds differ greatly is the strength of 
the muscles which move the wings. It may be assumed that the 
strength of these muscles corresponds with their weight. The 
relation between the weight of the pectoral muscles and that of the 
whole bird has been investigated among others by Legal and 
Reichel,? who found that the pectoral muscles weigh on an average 
about one-sixth of the whole bird; but that in different types of 
birds there may be considerable difference in this respect. For 
instance, in a House-Pigeon the proportion was 45 Riven, while 
in a Herring-Gull it was only +6=per-eent.” Some birds therefore 
have much more powerful wing-muscles than others. 
The shape of the wing, moreover, varies considerably also in 
different birds. Some, like the Swallow, have long and narrow 
wings, while others, like the Quail, have short and broad wings. 
The wings of some soaring birds, as Eagles and Vultures, are 
rounded at the points, and the primary feathers are separated from 
one another at their tips, giving a notched appearance to the end 
of the extended wings. A typically flying bird, such as a Falcon, on 
the other hand, has pointed wings with little separation of the tips 
of the primary feathers. These differences correspond to differences 
in the power and mode of flight. 
Birds, as well as all other animals that fly, may be divided into 
categories according (a) to the ratio between the sail-area and the 
weight, (b) to the strength of the pectoral muscles, and (c) to the 
shape of the wings. Of these categories or “types” Miillenhoff 
1 “Tie Grosse der Flugflichen.” Archiv fiir die gesammte Physiologie 
(Pfliiger’s), xxxv. (1885) pp. 407 e¢ seqg. Miillenhoff follows Harting, Legal and 
Reichel, Marey, and others in estimating the ratio between the sail-area of Birds 
and their weight by the formula A?/P?=c, in which A is the area (in square 
centimetres) of the out-stretched wings and tail as well as of the body, 
spread out on a flat, surface, while P is the weight of the bird (in grammes). 
The values found for o in different birds range from 2°85 (Golden-Eye) to 6-735 
(Barn-Owl). 
2 Verhandlungen der Schlesischen Gesellschaft fiir vaterlind-Cultur. Breslau : 
1882. 
