Mr. Yarrell on the Organs of Voice in Birds. 313 



which go off about half-way between this bulb and the inferior 

 larynx, to be inserted upon the os furcatorium. These muscles 

 are called ypsilo-tracheal by Baron Cuvier, from the form of the 

 bone upon which they are inserted. They seem peculiar to 

 those birds having enlargements of the tube, and figures of the 

 two last-mentioned tracheae will be found attached to Dr. La- 

 tham's Paper in the 4th volume of the Transactions of the Lin- 

 nean Society. 



I have mentioned the Gannet as differing from the Natatores 

 generally in being provided with a second pair of true muscles 

 of voice ; but the second pair in this bird differ materially from 

 the furculo-tracheal muscles already described as existing in the 

 three species of palmated birds having enlargements of the tube. 

 The trachea in the Gannet is uniform in size throughout, and fur- 

 nished with one strong pair of muscles, which, passing down the 

 side of the tube nearly the whole of its length, go off to be in- 

 serted upon the sternum as usual. Underneath and below these 

 there is another pair given off from the inner surface of the first, 

 which pass directly downwards, and are inserted upon the upper 

 surface of a spherical glandular protuberance fixed to the upper 

 or first half-circular bronchial cartilage. The membranous divi- 

 sion between the point or bone of divarication and this first ring 

 is considerable ; and the contraction of this second pair of mus- 

 cles shortens the bronchiae the whole depth of this division, pro- 

 ducing at the same time corresponding tension of the membrana 

 tympaniformis. The protuberances upon the bronchioe here no- 

 ticed are solid, unctuous in appearance, and probably perform 

 the office of bronchial glands. Tab. XVIII. Fig. 4, & 5, repre- 

 sent the lower portion of this trachea in two points of view. 



Tracheae possessing three pairs of true muscles of voice are 

 confined entirel}?-, as far as my observations have extended, to 

 one very large family only, the Psittacida ; and these muscles 



2 s 2 will 



