GENERAL REMARKS. 109 



wing. It is called the great pectoral muscle ; and, in 

 birds of powerful flight, those two muscles are heavier, 

 or contain more substance, than all the other muscles 

 in the body. The second muscles raise the wings, 

 and prevent them from turning on edge, which neither 

 of the other muscles could do without impeding the 

 freedom of their proper motion in working the wing 

 upwards and downwards at right angles to the axis of 

 the body. There is, however, a slight oblique motion 

 in the elbow joint of the wing, by means of which 

 this third or central muscle causes it to strike partially 

 forwards, at the same time that the great pectoral 

 muscle makes it strike downwards. 



Such are some of the motions of the more efficient 

 wings of birds, and such some of the instruments by 

 which they are performed ; but from the jer-falcon, in 

 which they are the most perfectly developed and the 

 most in accordance with the whole skeleton and other 

 structure, and therefore form, along with the most 

 predatory claws and beak, and the digestive organs 

 the best adapted for subsistence upon recent flesh, 

 the most direct means of arriving at the habit and 

 character there is a gradual decline of the efficiency 

 of the wings, as compared with the other active struc- 

 tures, until we come to the ostrich, which has only a 

 sort of rudimental flaps to steady it as it runs, the 

 penguin, whose rudimental wings seem to answer 

 only the same purpose in swimming, or the apteryx, 

 whose wings are covered by the skin, thatched by the 

 feathers, and seem to answer no purpose whatever. 

 But though there is this gradation, and though in as 

 far as the wings, and all those parts of the skeleton, 

 and the muscles which are connected with the wings, 

 are concerned, we can trace it with comparatively 

 little difficulty, yet it is so far from taking the habit 



