24 PRACTICAL ORNITHOLOGY. 



sound, which I found to be rendered louder and sharper when 

 the bronchi were contracted, so as to allow their membranes 

 to vibrate. A person present suggesting that the sound was 

 produced in the upper larynx, because it also was in a state of 

 vibration, I had the trachea cut across. On blowing into the 

 bronchi, I caused the same sound as before, but considerably 

 shriller, and could vary its tone from grave to sharp by stretch- 

 ing or contracting the bronchi. The sound was evidently pro- 

 duced by the tremulous motion of the bronchial membranes, 

 and especially of that part situated between the last ring of the 

 trachea and the first bronchial half ring. 



The muscles by which the bones of the larynx are moved, 

 so as to open and close the aperture of the glottis, and draw it 

 backwards or forwards, so as to modulate the voice, are, in the 

 Rook, the following : — 



1. The larynx is connected with the hyoid bone and tongue 

 by elastic tissue, but it has also a muscular connexion. As is 

 seen in Fig. 8, a pair of thin and slender muscles, the tliyro- 

 hyoidei, arise in front from the thyroid bone, and are inserted 

 into the basal part of the hyoid bone. Their action is to pull 

 the larynx forwards during deglutition, so as to draw the fore 

 part of the aperture of the glottis, Fig. 3, d, into the sheath, e, 

 which answers the purpose of the epiglottis in man. If the 

 larynx be fixed, it also draws back the tongue. 



2. The other muscles of the larynx are seen on its posterior 

 and superior part. The first may be named the thyro-arytenoi- 

 deus or apertor glottidis, Fig. 9. It arises from the appendages 

 of the thyroid bone, from part of the edge of the body of that 

 bone, and passes obliquely forwards and inwards to be inserted 

 into the inner edge of the arytenoid bone, and into the cartilage 

 by which it is margined. Its action is to separate the lips of 

 the aperture of the glottis. This muscle lies immediately 

 under the integument, or mucous membrane and papillre seen 

 atyy, in Fig. 3. The arytenoid bones are prevented from being 

 too widely separated by their anterior ligaments, e e, Fig. 5. 



8. The aperture of the glottis is closed by a pair of very small 

 muscles. Fig. 10, which arise from the anterior and upper 

 part of the cricoid bone, and are inserted along the inner edges 



