510 Mr. Yarre rt on the Organs of Voice in Birds. 
support the trachea, and serve to accommodate the tube to all 
the varied inflexions of the neck: they influence the length of 
the trachea as well as that of the bronchiz, and on account of 
their place of insertion have been named sterno-tracheal.. 
Tas. XVIII. Fig. 1. & 2. are a front and side view of a tra- 
chea furnished with one pair of muscles, in which the letters d, d 
mark the portion of each muscle going off to be inserted upon 
the sternum. Tas. XX. Fig. 1. represents the trachea of the 
Curassow (Craz Alector) with its singular convolution lodged 
between the shafts of the os furcatorium. Fig. 2. represents 
the posterior aspect of the same trachea removed from its natu- 
ral situation to show its single pair of muscles (d, d). 
Some of the birds possessing two pair of true muscles of voice 
may be considered as exceptions to a general rule, rather than 
otherwise, since they belong to those orders which usually pos- 
sess but one pair. | 
The Indian Crowned Pigeon, the largest example of the 
family, exhibits this second pair of muscles (Tas. XVIII. 
Fig. 3, e). ‘They are formed of a portion of the sterno-tracheal 
muscles, but taking a different direction. They proceed by 
- a narrow slip, from that point upon the tube where the first 
pair of muscles go off to be inserted upon the sternum, down 
the side of the trachea, to be attached externally to the mem- 
brane between the lowest ring of the tube and the first ring 
of the bronchia, as shown in the side view before referred to. 
By their contraction they shorten the flexible portion of the 
tube between their points of attachment, and produce tension 
upon the membrana tympaniformis. Our British Pigeons exhibit 
a few fibres in the same relative situation. 
The Wood Grouse is remarkable for its variation in the organ 
of voice from other Gallinaceous birds. The tube of the trachea 
is one fourth longer than the neck of the bird, and this excess 
| forms 
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