Mr. Yarrell on the Organs of Voice in Birds. 311 



forms a free and loose curve or fold within the skin (Tab. XXI. 

 Fig. 1, a). The first pair of muscles of large size are not at- 

 tached to the tube throughout any part of its length as in other 

 birds (Fig. 'i, d), but pass separately downwards, becoming 

 connected together below the convolution of the trachea, and 

 inserted upon the os fiircatorium or merrythought, at the angle 

 formed by the junction of the two shafts of that bone. About 

 the commencement of the lower third portion of these mus- 

 cles, each of them sends off a narrow slip downwards, which 

 becomes attached on its own side to a strong membranous sheath 

 that invests and strengthens the lower portion of the trachea 

 (Fig. 1, e), ultimately quitting the tube above the point of diva- 

 rication in the ordinary way, to be inserted upon the sternum, 

 becoming the true sterno-tracheal muscles ; the first pair, from 

 their place of insertion, being called furculo-tracheal, of which 

 we shall hereafter find further examples. Tab. XXI. Fig. 1, is a 

 representation of the trachea and its muscles in this bird, in 

 which another peculiarity will be observed. By the contraction 

 of the first pair of muscles, marked c?, the glottis may be drawn 

 downwards two inches below its ordinary or true situation upon 

 the pharyngeal portion of the os hyoides : the length and flexi- 

 bility of the tube of the trachea itself, and the power of with- 

 drawing the glottis just noticed, forming a considerable cavity 

 by the elongation of the pharynx, are principally instrumental 

 in producing the very powerful voice this bird is known to pos- 

 sess. The muscles for elevating and directing the glottis to its 

 ordinary situation are also shown. 



Among the Natatores, which I have stated generally as pos- 

 sessing but one pair of muscles of voice, there are four excep- 

 tions known ; the Velvet Duck, the Golden-eye, the Red-breasted 

 Merganser, and the Gannet ; these birds possess a second pair 

 of muscles of voice. 



VOL. xvi. 2 s I'he 



