THE MACHINERY OF FLIGHT 73 



continued exertion are rich in sarcoplasm, which 

 would seem somehow to supply food to the muscle 

 proper, to the contractile fibrillse ; at any rate this 

 is a reasonable theory that explains the facts.* 

 Now the muscle which in strong-flying birds is 

 reddest and, in section, most ridged and granulated, 

 is the Great Pectoral that lowers the wing. This 

 is a muscle of great size, as I have already pointed 

 out, and its output of unflagging energy is truly 

 astonishing. The Elevator muscle is paler and 

 smoother, and almost certainly of far inferior quality. 

 Much less is demanded of it. As soon as the bird 

 has got up pace, the resistance of the air lifts the 

 wing, and the Elevator has little to do. In fact the 

 great Depressor may claim to lift the wing, since to 

 it is due the velocity which relieves the Elevator of 

 its work. In the Blackcock, the Red Grouse and 

 the Ptarmigan, the paleness of the Elevator forms 

 a striking contrast against the rich red of the great 

 muscle under which it lies. Among birds whose 

 flight muscles I have examined, the Guillemot is 

 the only one whose Elevator is as rich a red and 

 almost as stringy as the Depressor. Is this explained 

 by the fact that the bird uses his wings in swimming ? 

 Has he to raise his wings in the water by muscular 

 effort ? And is this due to the fact that when he 

 swims he has less pace than when he flies ? In the 

 Chicken, since it seldom uses its wings, all the 

 Pectoral muscles are very pale and smooth. The 

 wild Jungle Fowl, from which our domestic bird 

 springs, uses its legs far more than its wings, and, I 

 believe, domestication has not much altered the 



* See Starling's Physiology on quality of muscle (pp. 87, 88). 



