re is a
slight, almost negligible, upward movement of the quadrate. The
movements of the various bony elements were observed on a skull that
had been made flexible by boiling in water for a minute as suggested by
Beecher (1951a:412).

Also in the columbids the naso-frontal hinge is not constructed in the
same manner as it is in many other birds as there is not a simple hinge
across the entire base of the beak. In fact, there is no true hinge at
all in the area of the nasals, but those bones are extremely thin and
they bend or flex under pressure. Actually, the hinge is double or
divided. One part is on either side of the nasals. The hinges are
situated at the posterodorsal tips of two thin processes of the
maxillary bones and the appearance is not unlike that of half a span of
a suspension bridge having the hinges at the tops of the towers.
Several other species of birds share this type of hinge construction
with columbids.

The movement of the lower jaw is, of course, the primary operation
involved in opening the mouth. The lower jaw possesses a deep fossa at
its posterior end, or on its posterodorsal surface, which articulates
with the body of the quadrate bone. The length of that part of the
mandible extending behind the articulation is directly correlated with
the resistance offered the mandible in opening, since it is on the
posterior extension that the depressor of the lower mandible inserts.
The larger the muscle the more surface is needed for attachment. Also
the added length of the mandible posterior to the articulation serves
as a lever in opening the mandible, and the fulcrum is moved relatively
farther forward.

In birds lacking resistance to abduction of the lower mandible, as in
doves, it is nevertheless necessary for a slight postarticular process
to remain for the insertion of a small depressor muscle which, as
mentioned previously, is necessary to counteract the relaxed adductor
muscles of the lower jaw.

There are many exceptions to the rule that birds have kinetic skulls,
and usually a secondary fusion and reinforcement of bones around the
hinge has limited or eliminated all movement. Sims (1955) describes the
Hawfinch's immobile upper jaw, which is used as a powerful press in
cracking the stones of fresh fruit. Skulls of woodpeckers have been
modified somewhat in the same manner as a result of their foraging and
nesting habits (Burt, 1930).

The two most distantly related members of the genera