Page 67 - The Origin of Birds and Flight

Head and Neck:
The most evident features of the avian skull are the
absence of teeth and of the heavy jawbones needed to
support them. In birds, the chewing or masticatory
action occurs in the crop, one of the two chambers in
the stomach and which constitutes a large part of the
weight in the bird’s center of gravity. This balance
causes flight to be less tiring. In addition, birds lack
dense facial bones, and their beaks have a woven net-
like structure that reduces weight without causing a
loss of strength.

Wing and Hand:
The arm structure includes the upper arm bone, orhumerus, forearm bone (radius), ulna
and wrist bone (carpal). In birds, the main flight muscles are attached to the arm mus-
cles only, which makes them highly force-resistant. The humerus is short and strong, so
as to provide the essential resistance. Protrusions on the elbow bone are where second-
ary flight feathers are attached to the wing bones. The bones in the bird’s wrist and met-
acarpal bones are fused in such a way as to support the primary flight feathers.

Pectoral Belt:
The bones in the arm and leg provide support. The pro-
truding sternum is one of the component of the skeleton
that makes wingbeats possible, supporting the muscles
that move the wings up and down.
The triosseal canal forms a kind of frame for tendons
attached to the muscles that lift the wing Wide, fused
scapula bones (collectively known as the furcula) make
it possible for the muscles that contract significantly
during flight to expand again, and this structure is found
only in birds.
Broad coracoid bones provide support for the breast
against the stresses of the flight muscle, to protect the
breastbone from suffering severe damage during flight.