Encyclopaedia Britannica > Volume 3, Anatomy-Astronomy

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ANATOMY.
Compara¬
tive
Anatomy.
85
young birds and those recently hatched ; for the bones two external ones, which corresnnnH m „
are very early united, and in the adult bird the cranial arches of the Mammalia and whirh o h Zyg]0mJtlC
sutures are invanably obliterated. Thus, in the domestic are articulated to the quadrangular bone which moves on
fowl and turkey the scull is one piece ; and the only trace the temporal before the eir Th« * " • wmcft ™oves on
of suture that remains is a linear depression in the mid- which have been already stated tn ° inter™edialf ones>
die of the frontal bone, indicating the original formation rygoid processes,andwhkh are paralHare^lac^d benla'th
m ^ l'alves- In rece,"tly bird, also, the the septum of the orbits, and ale articulated by the“ nos
tenor extremities with a small bone, variable in shape
but named omoid by Herissant, which is also articulated
with the quadrilateral. From this arrangement results
a singular species of broken lever, not dissimilar to the
parallel joint of the piston and lever of the steam-eno-ine
and the effect of which is, that whenever the lower5jaw
is depressed by its proper muscles, it necessarily causes
sphenoid is separated from the occipital bone by a trans¬
verse suture, extending from the one ear to the other.
The occipital bone is at the same time a ring, consisting
of four parts ; a superior, two lateral, and an inferior
which is small. The sphenoid, which forms the greater
part of the base of the cranium, is nearly trilateral, with
a small anterior process, to which the palatine arches are
If has no pterygoid processes, and does not the quadrilateral bo^ne^ p rform’a si ghrSUyTo8
itenor aperture of the nostr s. The lem- iioo ,„ ...u:„u e s "■ rotatory mo-
Facial
bones.
articulated. ^ 7
touch the posterior aperture of the nostrils. The tem
poral bone, though void of zygomatic process, has a
pointed style, which contributes to form the posterior
margin of the orbit. The frontal bone, after covering
part of the cranium, is continued forwards in a broad, thin
plate, which forms the vault of the orbits, while these ca¬
vities are separated by a thin vertical bony plate which
descends at right angles from the frontal bone, and is con¬
nected behind with the sphenoid. The long eminences
observed on the heads of the cassowary, curlew, pintado,
and some species of hocco, are produced from this supra¬
orbital part of the frontal bone ; and their interior, which
consists of loose diploe, communicates with that of the
same bone.
I he face in birds is rarely so firmly consolidated as the
cranium. It is composed of two lacrymal bones, forming
the anterior margins of the orbits, and united on the me¬
sial plane; two nasal bones anterior to the lacrymal; two
bones corresponding to the superior maxillary, and form¬
ing the external lateral parts of the upper half of the bill;
two inter-maxillary bones ; two anterior palate bones, cor¬
responding to those of the Mammalia ; two posterior pa¬
late bones corresponding to the pterygoid processes of the
tion, m consequence of which, by means of the omoid
bone, the upper jaw is at the same time elevated on the
elastic plates; and as soon as the lower jaw is raised, the
elasticity of these plates forces down the superior one.
The upper jaw is immovable in a few instances only,
and of these the calao or rhinoceros bird is one.
The breast bone (sternum) is a trilateral, boat-shaped Sternum
bone, concave internally, convex with a middle longi-or breast,
tudinal crest externally, with the base of the trianglebone'
above, and the apex, which is also incurvated backwards,
below. The middle longitudinal crest, which is occa¬
sionally named the keel (carina), is shaped something
like a spherical triangle, with the broadest side above, the
base before, and the apex behind; and its prominence
forms large spaces on each side for the attachment of the
pectoral and other muscles used in flight. In the male
wild swan (anas cygnus), in some species of curlew, in the
crane, and in the guinea-fowl, this crest forms a cavi¬
ty for the reception of the windpipe. In the ostrich and
cassowary, which do not fly, the sternum is void of crest,
and is merely arched strongly.
The ribs, which rarely exceed 10 pairs, may be distin-The ribs,
guished into sterno-vertebral and vertebral. Though the
, .. , . a 1 y ~ r—w.v, guioncu iulu ateuiu-vtirieurai ana verteorai. inouari the
of nn°ld ; and v1?! kT JaWi a Parfboloid bone’ consisting latter are generally before, they are sometimes also be-
of two ram* united before, where thev are covered hv the hind Tho nQv-i-QLroi : . i-
I’he quad-
lateral
kone.
of two rami united before, where they are covered by the
horn of the lower half of the bill. Besides these, there is in
the whole class an irregular-shaped bone, common to the
cranium and lower jaw, and connecting these two together.
This bone, which has been rather improperly named the
1 1 j , A r v sLcuiu-Lusua cartilages or tne iviammalia by umtino-
square, quadrangular, or quadrilateral bone (os quadratum), the rib to the sternum. The ribs of birds, however are
COIlSlStS of hnriv with r»nrvilin^Qr hz-Jl/Avnr i• . • • i v v . - . ?
hind. The vertebral end terminates in two diverging pro¬
cesses, one of which is articulated with the vertebral body,
the other with the transverse process. The sternal extre¬
mity consists of a bony process, which performs the part of
the sterno-costal cartilages of the Mammalia by uniting
laxillary
nies.
consists of a body with curvilinear hollow margins, termi
nating in two elevated and rather pointed processes, one
of which is connected with the cavity named tympanum,
while the other, projecting into the orbit, affords attach¬
ment to several muscles. The anomalous character of
this bone has perplexed several of the most distinguished
zootomists; and while Geoffroy gives it the name of os
Tympano-styloidewn, Spix considers it analogous to the
annular process of the temporal bone, which in the human
. ^ »» V, * J ClJl C
further distinguished by presenting near their middle a
flat long process, projecting from the rib backwards at an
acute angle, and resting on the rib immediately below, so
that each rib is supported not only on the vertebrae and
sternum, or the vertebrae alone, but on the next rib below.
These processes are obliterated in the lower ribs.
The coxal bones constitute one piece wfith the sacrum Basin or
and lumbar vertebrae. The ischial portion is united withPelvis-
the sacrum, and the ischiatic notch is converted into a
r A. • 1 .T All. XlU.llia.lI LUC 5
he'^LTXi.iM CarUS regfdS 11 Is, repr-Se uting I'0'6' The part which corresponds to the os piibis of the
aiirt h b ?rsar eresembance'nshape is not consolidated before so af to form a
‘ one of its connections. .cvmrJvfrcic ™ _
and in one of its connections.
Both maxillce are void of teeth; but the hard, horny
matter of the bill covering the margins and extremities
of each jaw, and constituting the mandibles (mandibula),
is manifestly constructed to perform for Birds what teeth
do for the Mammalia. But the most remarkable pe¬
culiarity of the facial bones of this class is, that the
. ~ l/W 1W11U a
symphysis, but proceeding directly backwards, terminates
in a styloid process, variable in length and slenderness.
The only exception to this mode of structure occurs in the
ostrich, in which the pubal bones are united below. The
infra-pubal or oval hole is present in the whole class not¬
withstanding. It is worthy of remark, however, that in
unner Gw nflmDo T young birds this and the ischial aperture are still notches,
ritv V ms=S, f m°reff °r m°tl0n' In.the maj°- in consequence of the deficient ossificatiofi of the parts,
to the crant?m ! HlS 18 eSJte,d. by theJaw being united The direction of the pelvis in birds is nearly that of
plates • but in tli ^ means 0 lm’ flexible, elastic, bony the spine, that is, obliquely backwards, and deviating but
d sthmt mV Parrotlfamdy the upper jaw is entirely little from the horizontal line.
The incp ^0nnecte by a proper articulation. The wings or thoracic extremities are connected to the
divided intn A 6 atine. surface of the upper jaw is trunk by three bones, the collar-bone or clavicle, the sra-Collar-
lancies, which diverge backwards. The pula, and the bifurcated bone. The collar-bones, which bone.