On the structure of the beak and its muscles in the crossbill (Loxia curvirostra) / by William Yarrell.

  • William Yarrell
Date:
[1829]
Catalogue details

Licence: Public Domain Mark

Credit: On the structure of the beak and its muscles in the crossbill (Loxia curvirostra) / by William Yarrell. Source: Wellcome Collection.

Provider: This material has been provided by The Royal College of Surgeons of England. The original may be consulted at The Royal College of Surgeons of England.

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    To those who have not made the habits and economy of birds an object of investigation, it may be necessary to state that our two species of Crossbill are the only British birds that exhibit or seem to require any lateral motion of the mandibles, and it is the object of this paper to describe the bony structure and muscles by which this peculiar and powerful action is obtained. It may be necessary to premise that Mr. Townson in his Observations in Natural History and Physiology, has devoted a chapter to the struc- ture of the bill of the Crossbeak, some extracts from which will be introduced in this notice ; but to show that I am not occupying the valu- able pages of the Journal with a tale twice told, the first sentence I select is as follows. Speaking of the beak, he says, I ought now to give the anatomy of it, and I wash it were in my power; but on the muscles, by which the motions I have spoken of are performed, I find scarce any memorandums in my portfolio. The beak of the Crossbill is altogther unique in its form; the mandi- bles do not lye upon each other wi\h their lateral edges in opposition as in other birds, but curve to the right and left, and always in opposite direc- tions to each other. In some specimens the upper mandible is turned to the right, the lower mandible curved to the left; in others, the position of the mandibles is reversed as to their direction. In the specimen I examined the upper mandible curved downwards and to the left, the under portion turned upwards and to the right, as the figures 1 and 2, plate xiv, wiU demonstrate. When holding the head of this bird in my fingers, I found I could bring the point of the imder mandible in a line underneath and touching the point of the upper, but not beyond it towards the left side, while on its own side the point passed with ease to the distance of f of an inch. The upper mandible has a limited degree of motion on the cranium, the superior maxillary and nasal bones being imited to the frontal by flexible bony laminae. The form as well as the magnitude of the processes of some of the bones of the head are also peculiar to this bird. The pterygoid processes of the palatine bones are considerably elon- gated downwards, as shewn at figure 3, letter a, to afford space for the insertion of large pterygoid muscles. The os omoideum on each side
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