flattened horizontally and supported by the anterior process of the os hyoides, which forms a ridgeN along
the middle of its inferior surface. At about four inches from the extremity of the horny lamina the margins
become obliquely notched, and these notches, becoming deeper and closer together towards the extremity,
occasion the bristled appearance on each side of the tongue. These bristles, Mr. Vigors observes, were
«generally applied to the morsels of food whilst held between the mandibles previously to being swallowed.
The cornua of the os hyoides are 1± inch in length. The trachea is narrow, and simple in its structure, the
rings somewhat flattened and decreasing in diameter towards the inferior extremity, from which a single pair
of muscles pass off to the sternum. The length of the lower fourth of the tube, and the state of tension in the
bronchia, are regulated by a pair of small muscles, which, arising from the sides of the tracheal cartilages, are
inserted into the bone of divarication at the extremity of the trachea : and that this part of the tube is
subjected to variations in length is indicated by the tortuous character of the recurrent nerves attached to the
sides of the trachea at this part. The lungs are small in proportion to the size of the bird, but of the usual
form and structure. The abdominal air-cells are of small size. The heart is of a more oblong form than
in general ; its apex, as it were, truncate ; its length 1 inch.
The pectoral muscles, as in the Psittacidoe, are but feebly developed, and the keel of the sternum is of
moderate size, not projecting more than half an inch from the plane of the bone. The sternum has four
notches at its posterior margin. The clavicles, or lateral halves of the furcula, are here, as in the Psittacidoe
and Struthionidoe, separate ; they are 1 inch in length, slender, pointed at their lower ends, and joined to each
other and to the sternum by ligament only.
The peculiar motions of the tail called for a particular examination of that part. It is difficult to state
the precise number of the caudal vertebroe in consequence of the terminal ones being anchylosed, requiring
for this purpose the examination of a young specimen at a period before the anchylosis takes place. In the
skeleton of a Black-billed Toucan which I have examined, it would appear that three vertebroe are thus
anchylosed, making the entire number of coccygeal vertebroe nine. The Woodpecker has also nine caudal
vertebroe, and this seems to be the greatest number found in birds. The first six of these vertebroe in the
Toucan are articulated by ball-and-socket joints, the ball and the socket being most distinct in the last two
joints. That between the sixth and the anchylosed vertebroe is provided with a capsule and synovial fluid ; the
others have a yielding ligamentous mode of connexion. The spinous processes of these vertebroe, both
superior and inferior, are of moderate size, but smallest in the sixth, where the greatest degree of motion
takes place. The transverse processes, on the contrary, are large and broad, so as almost wholly to prevent
lateral motion. The first of the anchylosed vertebroe is broad and flat and of a rounded form, supporting the
two coccygeal glands : the last of these processes is compressed laterally, and of the ordinary ploughshare
form. The caudal vertebroe can be inflected dorsad till their superior spines are brought into contact with the
sacrum ; in the opposite direction they can scarcely be bent beyond a straight line : and it is to this structure
of the bones and joints that is to be attributed the capability in the Toucan of turning its tail upon its back
(as represented in the Zoological Journal, vol. ii. pi. xv.), the muscles presenting comparatively few
peculiarities, since the motion alluded to is remarkable rather for its extent than the vigour with which it is
performed.
The principal elevators of the tail are the sacro-coccygei superiores (sacro-sus-caudiens of Vicq d’Azyr).
They arise from two longitudinal ridges on the inferior and convex part of the sacrum, and are inserted into
the superior spines of the first six vertebroe by detached tendons, terminating broadly in the anchylosed vertebroe.
The principal antagonists of these muscles, sacro-coccygei inferiores (sacro-sous-caudiens of Vicq d’Azyr), pass
over the first five vertebroe and terminate in the sixth and anchylosed vertebroe : their origins are wider apart
than in the preceding pair of muscles, coming off from the margins of the sacro-sciatic notches. In the
interval are situated small muscles passing from the transverse processes to the inferior spines of the first six
vertebroe.
From the limited nature of the lateral motions of the tail the muscles appropriate to these movements
are feeble, especially in comparison with those which are observed in the birds that spread their tail-feathers
in flight, in order to regulate their course during that vigorous species of locomotion. These muscles
are in number two on each side, arising from the posterior extremities of the ischia, and inserted into the
expanded anchylosed vertebras. From the disposition of these muscles it is obvious that after the proper
elevators have raised the tail to a certain height, they also become dorsad of the centre of motion, combine
their forces with the elevators, and by this addition of power terminate the, act of throwing up the tail by a
jerk: Mr. Vigors in his observations on the living animal observes, that “ in these movements the tail
seemed to turn as if on a hinge that was operated on by a spring.”
The osseous portions of the mandibles of the Toucan are disposed in a manner adapted to combine with
the great bulk of those parts a due degree of strength and remarkable lightness, and the bony structure is
consequently of a most beautiful and delicate kind. The external parietes are extremely thin, especially in
the upper beak : they are elastic, and yield in a slight degree to moderate pressure, but present considerable
resistance if a force is applied for the purpose of crushing the beak. At the points of the mandibles, the
outer walls are nearly a line in thickness ; at other parts, in the upper beak, they are much thinner, varying
from l-30th to l-50th part of an inch, and in the lower beak are from l-20th to l-30th of an inch in
thickness.
On making a longitudinal section of the upper mandible, its base is seen to include a conical cavity, about
two inches in length and one inch in diameter, with the apex directed forwards. The walls of this cone
consist of a most beautiful osseous network, intercepting irregular angular spaces, varying in diameter from
half a line to two lines. From the parietes of this cone, a network of bony fibres is continued to the outer
parietes of the mandible, the fibres which immediately support the latter being almost invariably implanted
at right angles to the part in which they are inserted.
The whole of the mandible anterior to the cone is occupied with a similar network, the meshes of which
are largest in the centre of the beak in consequence of the union which takes place between different small
fibres as they pass from the circumference inwards. It is remarkable that the principle of the cylinder is
introduced into this elaborate structure: the smallest of the supporting pillars of the mandibles are seen to be
hollow or tubular, when examined with the microscope. The structure is the same in the lower mandible,
but the fibres composing the network are in general stronger than those of the upper mandible.
The medullary membrane lining these cavities appears to have but a small degree of vascularity. Processes
of the membrane, accompanying vessels and nerves, decussate the conical cavity at the base of the beak. The
principal nerves are two branches of the fifth pair, which enter at the lower part of the conical cavity, and
diverge and ascend as they pass forwards to the end of the bill, giving off branches, which are distributed to
the horny covering, and supply it with sensibility.
The air is admitted to the interior of the upper mandible from a cavity situated anterior to the orbit, which
communicates at its posterior part with the air-cell continued into the orbit, and at its anterior part with the
maxillary cavity. The nasal cavity is closed at every part, except at its external and internal apertures, by the
pituitary membrane, and has no communication with the interior of the mandible.
The organ of smell is confined to the base of the upper jaw. The canal, which is traversed by the air and
odorous particles in inspiration, forms a sigmoid curve in the vertical direction. The external orifice is on
precisely the same perpendicular line as the internal one. It is situated at the posterior surface of the upper
mandible, where it is raised above the level of the cranium ; the orifice is consequently directed backwards,
secure from all injury that might happen to it in the act of penetrating dense or interwoven foliage.
The olfactory canal is at first of almost a cylindrical form, and about two lines in diameter. It passes
forwards for about half an inch, receiving from the mesial aspect the projection of the first spongy bone; it
then bends downwards and backwards, and is dilated to admit the projections of the two other spongy bones :
from this point it descends vertically to the palate, at first contracted, and afterwards dilating to form the
internal or posterior orifice. The first or outermost spongy bone is almost horizontal, and has its convexity