IV. THE MUSCLES OF THE AIR PASSAGES. 



As in the vast majority of birds, the rings and half- 

 rings of the trachea of the Raven are completely ossified 

 in the adult individual. This applies also, with equal 

 truth, to the several parts of the superior larynx. These 

 cricoid bones and the pair of arytenoid bones are so well 

 known as to require no special description from me here. 

 Their arrangement is very well shown in Fig. 10, where 

 they are represented, in situ, double the size of life. 



Anteriorly, the upper larynx is composed of one shield- 

 shaped osseous plate, the thyroid, which rests upon the 

 upper side of the second basibranchial, in the fork of 

 the greater cornua of the hyoid. 



This plate is also seen in Figs. 9 and 10. 



The bronchial half-rings, and those of the lower larynx, 

 likewise ossify, but not quite so completely as do the 

 tracheal rings above them. 



In the Raven we have devoted to the superior larynx 

 two muscles — 



28. The constrictor-glottidis. 29. The thyreo-arytenoideus. 



And to the lower larynx seven more, viz. — 



30. The tracheo-lateralis. 34. The bronchialis posticus. 



31. The broncho-trachealis posticus. 35. The bronchialis anticus. 



32. The broncho-trachealis anticus. 36. The sterno-trachealis 



33. The broncho-trachealis brevis. 



