45 
The beak of the bird serves as both hand and mouth; the apex of the wedge, m 
these functions, is driven against resisting bodies sometimes of considerable hardness. 
In all birds the opening and closing of the bill are acts of prehension, In many birds 
these latter movements are not limited to the lower jaw, but a mechanism exists for 
raising the upper jaw as well, The joint between the base of the bill and the cranium 
is made flexible by diverse modifications. ‘The tympanic is fashioned in relation there- 
with; it is connected by two beams or columns of bone, on each side of the skull, with 
the fore part of the upper jaw. The outer beam, commencing forward at the side of 
the maxillary, is continued by the malo-squamosal style to the outer side of the trans- 
versely expanded lower part of the tympanic. The inner beam, commencing by the 
palatal process of the premaxillary, is continued backward by the palatine and ptery- 
goid bones to the inner side of the lower end of the tympanic. Any swinging to and 
fro of this bone upon its single or double upper ball-and-socket joint is transferred 
to the “core” by the four beams converging thereto. ‘The action of the outer beam 
upon the maxillary is conjoined with that of the lower beam upon the premaxillary 
by the overlapping broad palatal plate of the maxillary, which is more or less con- 
fluent with the palatine and premaxillary bones beneath. 
The movements of the mandibular part of the bill are transferred by the long bar- 
like rami of the lower jaw to the lower end of the tympanic, with which those rami 
are movably articulated by a combined double ball-and-socket and also trochlear 
articulation. 
When the tympanics are swung forward they communicate that motion by their six 
converging bony bars to the upper and lower cores, raising the former, depressing the 
latter; in short, opening the mouth. When the tympanics swing backward, opposite 
movements are transferred forward by the connecting bars, and the beak is shut. 
But when in this state it is used (as by the Woodpecker) as a pick or wedge, the 
strength of the blow transferred backwards by the three divergent pairs of bars is met, 
not by a rigid basis, which might have involved fracture of those bars or of some ot 
them, but by a yielding one, as in the butts with elastic buffers terminating a railway 
line, for arresting and receiving the shock of a train. 
The beak as a whole, and especially its outward and visible portions, lave suggested 
to ornithologists characters of groups with good and accepted descriptive terms: the 
modifications of a part of the mechanism, a single beam, seem inadequate to sustain 
new nomenclature. 
‘The basisphenoid (Pl. V. fig. 5, 5) in advance of the ridge or process which under- 
hangs the bony outlets of the Eustachian tubes loses breadth, and seems narrowest where 
impressed by the abutting ends of the pterygoids (24). 
‘The postarticular end of the mandible of Didus differs from that in most Columbide 
in not being abruptly truncated, but produced in the form of a short right or rather 
open angle with the apex obtuse (PL I.). That of Pezophaps (Pl. IV. tig. 1) is more 

