same cause has not primarily determined the
development of these plumes. The immense tuft of golden plumage in the
best known birds of paradise (Paradisea apoda and P. minor) springs
from a very small area on the side of the breast. Mr. Frank E. Beddard,
who has kindly examined a specimen for me, says that "this area lies
upon the pectoral muscles, and near to the point where the fibres of the
muscle converge towards their attachment to the humerus. The plumes
arise, therefore, close to the most powerful muscle of the body, and
near to where the activities of that muscle would be at a maximum.
Furthermore, the area of attachment of the plumes is just above the
point where the arteries and nerves for the supply of the pectoral
muscles, and neighbouring regions, leave the interior of the body. The
area of attachment of the plume is, also, as you say in your letter,
just above the junction of the coracoid and sternum." Ornamental plumes
of considerable size rise from the same part in many other species of
paradise birds, sometimes extending laterally in front, so as to form
breast shields. They also occur in many humming-birds, and in some
sun-birds and honey-suckers; and in all these cases there is a wonderful
amount of activity and rapid movement, indicating a surplus of vitality,
which is able to manifest itself in the development of these accessory
plumes.[133]
In a quite distinct set of birds, the gallinaceae, we find the
ornamental plumage usually arising from very different parts, in the
form of elongated tail-feathers or tail-coverts, and of ruffs or hackles
from the neck. Here the wings are comparatively little used, the most
constant activities depending on the legs, since the gallinaceae are
pre-eminently walking, running, and scratching birds. Now the
magnificent train of the peacock--the grandest development of accessory
plumes in this order--springs from an oval or circular area, about three
inches in diameter, just above the base of the tail, and, therefore,
situated over the lower part of the spinal column near the insertion of
the powerful muscles which move the hind limbs and elevate the tail. The
very frequent presence of neck-ruffs or breast-shields in the males of
birds with accessory plumes may be partly due to selection, because they
must serve as a protection in their mutual combats, just as does the
lion's or the horse's mane. The enormously lengthened plumes of the bird
of paradise and of the pea
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