30 SMITHSONIAN MISCELLANEOUS COLLECTIONS VOL. I43 



that may aid in raising the humerus is 15.9 percent of wing muscula- 

 ture in Cora gyps and 12.3 percent in Cathartes, while the supra- 

 coracoideus is only 6.50 percent of all wing muscles in Coragyps and 

 4.40 percent in Cathartes. In our studies we did not determine the 

 weight of all muscles used in raising the humerus, singling out the 

 supracoracoideus because it was the most important and was easily 

 dissected. 



It has been reported by Owen (see Shufeldt, 1890, p. 73) that the 

 supracoracoideus is almost the largest of the breast muscles in pen- 

 guins, guillemots, and gulls. It was pointed out that more effort was 

 required to raise the wings in the water than in the air. Divers such 

 as the grebe (Podiceps dominicus) that use their feet for propulsion 

 under water possess a small supracoracoideus. According to experi- 

 ments of Convreur and Chapeaux (1926), all birds that fly require 

 the muscles that raise the wings. After these muscles were severed 

 in pigeons, it was not possible for the birds to launch themselves into 

 the air or, when released from a height, to attain any semblance of 

 sustained flight. 



As was to be expected, the largest pectoralis was found in powerful 

 fliers, either those accustomed to long sustained flight or those that 

 fly for short distances at high speed. The pectoralis does its heaviest 

 work when taking off. 



Many more examples have been observed of heart differences in 

 relation to altitude than of flight muscle differences. The heart must 

 work almost continuously, being inactive only during diastolic pause, 

 while the flight muscles work intermittently. Why the altitude dif- 

 ference occurs in cuckoos and not in more active fliers is difficult to 

 understand. 



While the supracoracoideus appears to be of little importance in 

 many birds, it is largest in those birds that make quick takeoffs and 

 fly rapidly, such as tinamous, quail, hummingbirds, and doves. 



The remainder of the flight muscles, those of the shoulder, brachium, 

 and forearm, constitute only a small part of the total, and therefore 

 variation in these muscles, which is not great, may not be very sig- 

 nificant as a factor in flight. The muscles of the brachium are usually 

 heavier than those of the forearm, which would seem to indicate that 

 they do more work. 



Although the size of the muscle may determine the work that can 

 be accomplished, the continuance of the performance depends upon 

 the contained fat or other fuel, together with that which may be 

 brought to it by the blood. The amount of fat in the pectoralis super- 



