120 MR. R. OWEN ON THE ANATOMY OF THE CONCAVE HORNBILL. 
quadrato-maxillary articulation; and would at all times, when not drawn over the 
centre of motion by the backward movement of the lower jaw, contribute materially to 
support that part, and relieve the temporal muscle. Another strong ligament is destined 
to prevent dislocation backwards ; its origin from the zygoma is concealed by the pre- 
ceding ; it passes directly backwards to the posterior part of the condyle, or articular 
depression, of the lower jaw. 
On contemplating the maxillary muscles in situ, the first impression that arises is 
surprise at the disproportion they seem to bear to the vast apparatus they have to move ; 
but this disproportion is more apparent than real. The jaws, notwithstanding their mag- 
nitude, are rendered extremely light by the air-cells which are continued into them; 
their bony parietes do not exceed a line in thickness, except at the points, and the 
delicate columns by which these parietes are supported are themselves hollow. The 
disposition of these columns is remarkably beautiful; they are always perpendicular, 
or nearly so, to the part of the outer parietes in which they are implanted; and at the 
expanded base of the mandibles they radiate from a central cylinder, which is formed 
by a delicate osseous net-work ; and thus while the requisite strength is gained, light- 
ness is combined with magnitude. With respect to the attachments of the muscles, 
we may conclude that any apparent disadvantage in their insertion is sufficiently com- 
pensated by the superior energy of contraction with which the muscular fibres of birds 
are endowed. 
The bones and muscles of the cervical region of the spine have, however, an obvious 
adaptation in their development to the bulk of the entire head. 
The apparatus for flight! is more perfect than in the Toucan. The clavicles, which 
are separate in that bird, are here joined, forming a complete furculum, which, how- 
ever, is slender, being about a line in thickness at the junction. The sternum has two 
notches posteriorly, one on either side the keel, as in the Corvide, but they are shal- 
lower than even in that tribe: the greatest depth of its keel is an inch; the inferior 
margin of this part forms an almost straight line, and is not expanded laterally. 
I have already alluded to the extension of the air-cells among the soft parts ; and on 
an examination of the skeleton it appears that every bone, from the mandibles to the 
last of the coccygeal vertebra, from the clavicles and scapule to the last phalanw of the 
wings, from the femora to the last joint of the toes, and even every rib, is permeated 
by air. 
On comparing the anatomy of the Hornbill with that of the Toucan, we find a close 
resemblance in the structure of those organs which relate to the assimilation of nutri- 
ment. In both birds a simple gullet corresponds in its diameter with the capacity of 
the beak ; the proventriculus and gizzard in both equally manifest their adaptation to 
an omnivorous diet, the latter being neither so membranous as in the carnivorous birds, 
nor so muscular as in the granivorous. The short but ample intestines deprived of 
1 The noise of this action is heard from a considerable distance. 
