220 PHILOSOniY OF ZOOLOGY. 



The feathers of birds are annually renewed ; but the 

 change takes place at different intervals, in compliance with 

 the conditions of the season. We have seen a Bernacle 

 goose (shot 6th January 1819,) with the black feathers on 

 the neck in progress of moulting, while, on every other 

 part of the body, the plumage was complete. The quill 

 feathers, in particular, appear to drop off' at intervals, in 

 succession, and as there is seldom more than one of these 

 wanting in each wing at a time, the power of flight is but 

 little impeded. Nor are the outermost quill feathers first 

 shed, but usually the fourth or fifth, and in some birds the 

 innermost of the primaries. 



The bones of birds, although bearing a close resemblance 

 to those of quadrupeds, both with respect to number and 

 position, exhibit several peculiarities by which their skele- 

 ton may be recognised. The sutures of the bones of the 

 cranium, speedily become ossified after birth. At the 

 union of the upper mandible with the frontal bone, there 

 is a thin intervening osseous plate, by which, a con- 

 siderable degree of motion is admitted. The orbits are 

 separated, in some species, by a membranous, in others, 

 by an osseous septum, descending from the frontal bone. In 

 front of the opening of the ear, and attached to the tem- 

 poral bone, the os quadratum is situate. It occupies the 

 place of the zygomatic process ; on the side, it is articulated 

 Avith the slender cheek-bone, anteriorly with the posterior 

 palatine-bone, and inferiorly with the lower jaw. The an- 

 terior and posterior palatine bones, are more or less con- 

 nected with the inferior edge of the orbital septum. The 

 occiput is articulated with the spine, by means of one con- 

 dyle. 



The spine of birds is remarkable for the number of cer- 

 vical vertebras, varying in the different species from nine to 

 twenty- three. The lumbar vertebra^ are ossified in one 



