851 
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The ossa unguis are common to birds with mammalia, but 
appear to be more general in the former than in the latter: 
they are of considerable size, and must be distinguished from 
the superciliary bones which probably belong to the acci- 
pitres, or predacious birds, only. 
The jaws are wholly destitute of teeth. The superior 
maxilla, which is completely immoveable in mammalia, has, 
with a few exceptions, more or less motion in birds. It either 
constitutes a particular bone, distinct from the rest of the cra¬ 
nium, to which it is articulated, as in the psittaci (birds of 
the parrot kind); or it is connected into one piece with the 
cranium, by means of yielding and elastic bony plates; as is 
the case with birds in general. It is quite immoveable in very 
few instances; as in the rhinoceros bird. 
The bill is of extraordinary hardness in birds which tear 
their prey, as in eagles, or in those which have to bruise hard 
fruits, as parrots, or in those which penetrate the bark of trees, 
as the woodpecker, nuthatch, &c. 
This hardness is gradually diminished in those which take 
less solid nourishment, or which swallow their food whole ; 
and the bill becomes a portion of nearly soft skin in those 
which require a sense of feeling in the part to enable them to 
obtain their food in mud, or water, as in ducks, woodcocks, 
snipes, &c. 
One of the peculiar characteristic differences of the cra¬ 
nium of birds when compared to each other, consists in the 
mode of separation of the orbits, which are of great size in 
the whole class. In some they are separated by a membra¬ 
nous partition only; in others by a more or less complete 
bony septum. The relation which the nasal and palatine 
openings bear to the upper jaw varies much, even in the 
different species of the same genus. They are small in the 
stork, and on the contrary, so large in the crane, that the 
longest portion of the jaw appears to consist merely of three 
thin portions of bone, placed far apart from each other, and 
converging towards the point of the bill. 
The want of motion in the back of birds, (their dorsal 
vertebrae have the spinous, and even the transverse processes, 
often anchylosed) is compensated by a large number, and 
greater mobility of the cervical vertebrae; of which, to quote 
a few instances, the raven has 12, the cock 13, the ostrich 18, 
the stork 19, and the swan 23. 
The trunk of birds has fewer cartilaginous parts than the 
corresponding division of the skeleton in mammalia. That 
part of the spine which belongs to the trunk is short and 
rigid, and has no true lumbar vertebrae. Neither has any 
bird an os coccygis prolonged into a true jointed tail. 
The length of the neck increases generally in proportion 
to that of the legs; but in aquatic birds in a much greater 
proportion, since they have to seek their food below the sur¬ 
face of the water on which they swim. 
The cervical vertebrae are not articulated by plane surfaces, 
but by cylindrical eminences, which admit a more extensive 
motion, as they constitute real joints, instead of synchon¬ 
droses. Four or five of the upper pieces only bend forwards, 
while the lower ones are confined to flexion backwards. 
Hence the neck of a bird acquires that double bend, which 
makes it resemble the letter S. It is by rendering the two 
curvatures more convex, or more straight, that the neck is 
shortened or elongated. The great mobility of the neck 
enables birds to touch every point of their own body with the 
bill, and thus to supply the want of the prehensile faculty of 
the superior extremity. The atlas has the form of a small 
ring, which articulates with the head by only one surface. 
In proportion to the mobility of the neck of birds is the fixed 
state of the dorsal vertebrae, which are connected together by 
strong ligaments. The greater part of their spinous processes 
are consolidated into a single piece, which runs like a ridge 
along the whole back. The transverse processes terminate 
in two points, one directed anteriorly, the other posteriorly ; 
they meet those of the two other classes of vertebrae, some¬ 
times anchylosing with them, as the spinous processes do 
with each other. This structure is necessary to give steadi¬ 
ness to the trunk in the violent motions required by the action 
of flying. 
The pelvis of birds is chiefly formed by a broad and sim¬ 
ple os innominatum; the lateral portions of which are of 
different figures in the several genera; but instead of uniting 
below to constitute a symphysis pubis, they are quite distant 
from each other. The ostrich alone forms a remarkable ex¬ 
ception to this rule, inasmuch as its pelvis, like that of most 
quadrupeds, is closed below by a complete junction of the 
ossa pubis. 
Birds have fewer ribs than mammalia; the number never 
exceeds ten pairs. The false ribs, i. e. those which do not 
reach to the sternum, are directed forward; the true ones are 
joined to the margin of the sternum by means of small in¬ 
termediate bones. The middle pairs are distinguished by a 
peculiar flat process, which is directed upwards and backwards. 
The sternum of these animals is prolonged below into a 
vertical process, (crista) for the attachment of the strong pec¬ 
toral muscles. In the male wild swan (anas cygnus) and 
in some species of the genus ardea, as the crane, this part 
forms a peculiar cavity for the reception of a considerable 
portion of the trachese. The crista is entirely wanting in the 
ostrich and cassowary; where the sternum presents a plane 
and uniformly arched surface. This peculiarity of structure 
is accounted for by observing, that these birds have not the 
power of flying. The wings, which are very small, assist in 
balancing the body as they run. 
The wings are connected to the trunk by means of three 
remarkable bones. The clavicles, which are always strong, 
constitute straight cylindrical bones. Their anterior extre¬ 
mities are connected to the sternum by means of a bone pe¬ 
culiar to birds; viz. the fork-like bone, or, as it is more com¬ 
monly termed, the merry thought. The ostrich and casso¬ 
wary have indeed no separate furcula; but on either side of 
the front of the chest an elongated flat bone, consisting of a 
rudiment of the furcula, with the clavicle and scapula conso¬ 
lidated into one piece. 
The bones of the wing may be compared on the whole 
to those of the upper extremity in man, or the quadrumana ; 
and consist generally of an os humeri; two bones of the 
fore-arm ; two of the carpus ; two, which are generally con¬ 
solidated together, of the metacarpus ; one bone of the 
thumb; and two fingers; of which that which lies towards 
the thumb, consists of two phalanges, the other only of one. 
The most remarkable deviation from this structure is found 
in the fin-like wings of the penguin. 
The bony structure of the lower extremities is more simple 
in birds than in mammalia. In general it comprehends only 
the following bones, viz. the femur, the tibia, (to which, in 
some, is added a small, thin, closely adhering pointed fibula, 
that is separate in early life only), one metatarsal bone, and 
the toes. On the metatarsal bone of the domestic cock and 
other birds of the gallinaceous tribe, the spur is situated. The 
place of the patella is supplied, in many cases, by a process 
of the tibia. The tibia is immediately articulated with the 
metatarsus. There is, in most of this class, a peculiar pro¬ 
gressive increase in the number of phalanges of the toes: the 
great toe has two; the next, three; the middle one, four; 
and the outer one, five. 
Fig. 34. Skeleton of a falcon (falco nisus): f, cavity of 
the tympanum; Jc, orbit; l, superciliary process and bone; 
Ttif os quadratum; n, zygoma; o, scapulae; p, os humero- 
capsulare; q, head of the clavicle of the right side, that of 
the left being concealed by the humerus; r, furcula; s, ster¬ 
num; t, radius; u, ulna; v, the thumb; to, the metacarpal 
bone of the little, and x of the great finger of the wing; y, 
the little finger; z, the first, and a, the second phalanx of 
the great finger; b, aperture for the admission of air into the 
humerus; c, the upper, and c*, the lower iliac processes 
of the dorsal vertebrae; cl, the ileum; e, the ischium; c *, 
the ischiatic foramen; g, the os pubis; h, the last caudal 
vertebrae; i, tibia ; a, fibula; b, tarsus and metatarsus. 
The muscles in this class are distinguished by possessing a 
comparatively weak irritable power, which is soon lost after 
death; and by their tendons becoming ossified, as the ani¬ 
mal grows old, particularly in the extremities, but sometimes 
also in the trunk. 
Birds 
