30 NATURAL SCIENCE. July, 1893. 



joint, moved rather more than half-an-inch — the movement of the 

 sternum being almost too slight to measure. I do not wish to 

 represent this experiment as one of much value. However, the condition s 

 of flight were so far reproduced that the weight of the body was 

 hanging upon the wings, and so hindering the movement of the 

 breast, while leaving the back free ; but there was none of the 

 pressure — which during flight must be very great — of the wings 

 upon the coracoid bones and clavicles. But would not the only 

 effect of this pressure be to render the sternum and the bones united 

 with it still less ready to move ? 



It will be observed that I have said nothing upon the vexed ques- 

 tion of the action of the internal intercostals. They are so weak that the 

 result of their action, whatever it may be, cannot be a large factor in 

 the problem of respiration. When a bird is standing or running, it 

 is obvious that the back is fixed to the legs, so that it cannot rise and 

 fall. Clearly, then, the process of respiration must be different, and 

 if a bird be watched when it is filling and emptying its air-chambers 

 in order to utter a loud note, the moving forward of the breast may 

 be easily seen. As I have said, the main obstacle to its motion 

 during flight is, not its weight, but the tension and pressure at the 

 shoulder joint. With regard to the abdominal air-sacs, the raising 

 of the hinder-quarters by the legs, when the bird is standing, will 

 itself expand them. The air will be expelled by the contraction of 

 the abdominal muscles, which will draw the sternum inwards. In 

 connection with this, I may mention that Mr. F. E. Beddard has 

 found the oblique septum muscular in the puffin, and I myself have 

 confirmed the observation. When a bird is sleeping with its 

 breast resting upon the perch, or lying upon the ground with nearly 

 all its weight upon its. breast, it must adopt a method of breathing 

 similar to that employed in flight. Often geese and other birds, 

 while lying on their breasts, will exert a great deal of voice-power, 

 and then the rising of the hinder part of the back is distinctly visible. 

 The fore part may appear to rise a little, but this appearance is due, 

 I think, to" the raising of the ribs by the levatores costarum. The 

 legs, apparently, have no weight upon them, so that the back is not 

 held down as in standing. The muscles called into play must be the 

 external intercostals and the triangularis sterni. 



F. W. Headley. 



