310 Mr. Yakrell 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 bronchiae, and on account of 

 their place of insertion have been named sterno-tracheal. 



Tab. 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. Tab. XX. Fig. 1. represents the trachea of the 

 Curassow {Crax Alector) with its singular convolution lodged 

 between the shafts of the os furcatorimn. 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 (Tab. 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 or<>;an 

 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 



