100 CLASS AVES. 



able space for muscular play. The clavicles, or bones of the furca, 

 joined in the form of a V, separate each shoulder in the opposite 

 direction, and resist, with elasticity, the vigorous movements 

 which the action of flight requires. 



In the skeletons of birds, the vertebrae are found to vary con- 

 iderably. Thus, in the sparrow, which has the fewest, there 

 are nine cervical, and nine dorsal ; while in the neck alone of 

 the swan there are twenty-three. By the formation of a facette 

 attached to each of the cervical vertebrae, the neck is pre- 

 served in a curve, as its natural unrestrained position, while 

 the vertebrae of the back are either fixed to each other, or are 

 so bound together by strong ligaments, as to render the whole 

 series incapable of any inclination out of a straight line, an 

 arrangement which evidently has reference to the faculty of 

 flight, by affording a more effectual resistance to the muscular 

 power employed by the wings, because, in such birds as do not 

 fly, the spine is capable of a curve, or bend. 



The number of vertebrae in the tail varies also, in proportion 

 to the length of the organ in each genus. 



The large square plate, called the sternum, convex in front, 

 and concave behind, to which the muscles of the wing are 

 attached, covers the thorax and the abdomen. In front of 

 this is the laminar bone before mentioned, the size of which 

 is always proportioned to the power of flight of the species, and 

 in the ostrich, which does not fly, it is altogether wanting. On 

 each side of the sternum are some long pieces, called sternal 

 ribs, which connect it with the vertebral ribs, forming altoge- 

 ther a protection for the intestines. 



The omoplate is small, forming a parabolic arch, and placed 

 parallelly with the spine on the ribs. Its coracoid apophysis 

 forms a long and very strong bone, flatted from front to rear. 

 The clavicles are united above the sternum, in front of the 

 coracoid apophyses, forming one distinct piece. This provi- 

 sion is evidently to afford the clavicle a greater elastic force, 

 which tends to separate the two omoplates, when the bird puts 



