Mr. YARRELL on the Organs of Voice in Birds. 311 
forms a free and loose curve or fold within the skin (Tas. 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. 1, d), but pass separately downwards, becoming 
connected together below the convolution of the trachea, and 
inserted upon the os furcatorium 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. Tas. XXI. Fig. 1, isa 
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 d, 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 ane sich the glottis tc its 
ordinary situation are also shown. > . B 
- Among the Natatores, which I iin stated generally 
sessing but one pair of muscles of voice, bere i are four excep- 
tions known ; the Velvet Duck, the Golden-eye, the Red- breasted ; 
Merganser, and the Gannet ; these "es possess a seconda pa — 
of muscles of voice. 2: Eo 
~VOL. XVI. 25s 
