230 General Characters. BIRDS. General Characters. 
gence in these animals than in those of the preceding 
class. The bones forming the skull in birds, become 
completely united together at a very early period of 
life, so that the whole of the true skull {cranium) 
iLsually appears to be composed of a single bony piece 
without any of those sutures, which, in the Mammalia, 
mark out the separate bones of which the skull is com- 
posed. The facial bones, on the contrary, are gene- 
rally attached to the skull in such a way as to retain a 
certain amount of mobility; and this is so great in some 
species as to give the upper mandible the appearance 
of being articulated to the cranium. The jaws are 
prolonged into a beak of variable form, upon the upper 
surface of which, near the base, the nostrils are almost 
invariably situated; the internal partition between these 
is sometimes deficient, when the nostrils appear to form 
a narrow horizontal slit or passage, leading from one 
side of the beak to the other. The jaws bear no teeth, 
but are covered with horny sheaths, the form of which 
varies remarkably, according to the nature of the food 
upon which the creature is destined to subsist. The 
orbits, Avhich are always placed laterally, are seldom 
completely closed ; the partition separating them is 
often perforated (fig. 140). Beneath them on each 
side runs a slender process of the upper jaw, called the 
jugal hone, which passes backward until it reaches a 
small bone springing from the hinder part of the skull 
on each side close to the ear ; these, which are called 
the tympanic hones, furnish the points of articulation 
for the two branches of the loAver jaw. The occipital 
bone, situated at the lower part of the back of the skull, 
exhibits a large aperture for the passage of the spinal 
cord, and a single condyle or tubercle for the articula- 
tion of the skull with the first vertebra of the neck. 
This condyle is always very convex, and sometimes 
nearly globular — a structure which gives to tlie heads 
of these animals a great range and facility of move- 
ment. 
The neck in birds is of greater average length than 
in mammals, and even in those species which appa- 
rently have a short neck when clothed with feathers, 
the cervical region of the skeleton is usually much 
elongated. The number of vertebrre is never less than 
nine ; but most birds have from twelve to fifteen of 
these bones in the neck, whilst some have upwards of 
twenty. The neck is longest m some of the aquatic 
birds, such as the swans and flamingoes; the neck of 
the swan has twenty-seven vertebrre. The bodies of 
the vertebrae present a convex surface behind, and a 
concave one in front, an arrangement which gives great 
freedom of motion ; and in most birds we find the neck 
capable of describing very sharp curves, whilst the 
strong lateral processes of the vertebrae furnish suffi- 
cient points of attachment for the muscles which 
support the neck in its different positions, and enable 
the bird to dart its head rapidly forward in order to 
capture its prey. 
Of the dorsal vertebrae tliere are usually from eight 
to' ten ; but some birds have only six of these bones, 
while others have as many as eleven. They are gene- 
rally short and very firmly attached to each other, so 
as to form a solid column ; great firmness being requisite 
ui this part of the body, in order to give a proper sup- 
port to the vdngs. In some cases, indeed, the dorsal 
vertebrae are anchylosed. They are furnished Avith 
spinous processes both above and beloAv ; the latter 
serving to give attachment to the lungs, which, as 
already stated, are affixed to the inner surface of the 
chest. They are also provided with transverse pro- 
cesses for the articulation of the ribs, Avhich present 
tAvo articulating surfaces — one of Avhich is applied to 
the body of the vertebra, and the other to the trans- 
verse process. The ribs are flat bones composed of 
tAvo parts, united by a movable joint (fig. 135) ; the 
upper part Avhich articulates Avith the vertebral column 
is the true rib ; the loAver, Avhich is attached to the edge 
of the sternum, is analogous to the sternal cartilage 
in the Mammalia. It is by this arrangement that the 
movements of the chest, necessary for the inspiration 
and expiration of air, are performed. From the pos- 
terior surface of each true rib, at a variable distance 
fr’om its base, there springs a laminar process of greater 
or less length, which projects backwards and upAvards, 
so as to overlie the succeeding rib just above its laminar 
process (fig. 134). The object served by these pro- 
cesses is that of furnishing an additional bond of union 
betAveen the different ribs, so that the whole frameAvork 
of the chest acquires a gi'eat degree of firmness. The 
processes are very large in birds possessing great 
poAvers of flight (such as the haAvks), whilst in those 
Avhich aBe not remaikable for this faculty they are 
usually of small size, or even rudimentary (see fig. 135). 
The sternum, Avhich completes the bony frameAVork 
of the chest, is a large, more or less triangular bone, 
concave internally and usually very convex externally, 
where it is also furnished Avith a large crest or keel, 
serving to give attachment to tlie enormous pectoral 
muscles, by Avhich the Avings are made to strike doAvn- 
Avards upon the air. In birds noted for a very poAverful 
flight, this keel is of great size, as might be anticipated; 
Avhilst, in the ostrich and some other birds Avhose Avings 
are so small as to be incapable of raising them into the 
air, the sternal keel is entirely deficient. The edges 
of the sternum, as already stated, give attachment to 
the sternal ribs ; at its anterior part it is provided Avith 
articular surfaces for the reception of some bones 
connected Avitli the wings, to which we shall have to 
allude further on. 
The lumbar vertebrae, which in tlie Mammalia 
ahvays retain a certain amount of mobility, are here 
completely amalgamated together, and Avith the sacral 
vertebrae, form a single piece to which the pelvis is 
attached. The latter is greatly elongated, advancing 
so far as often to conceal a portion of the last ribs (see 
figs. 135, 136) ; but its inferior arch is not closed, as is 
the case in the Mammalia. The only ImoAvn exception 
to this rule is to be found in the African ostrich. The 
posterior limbs are articulated to the sides of tlie pelvis 
by a ball and socket joint, as in the mammals. The 
sacral vertebrte are succeeded by tliose of the short 
tail, which are of small size, and vary from six to nine 
in number. The last vertebra is usually larger than 
the others, and often placed so as to rise perpendi- 
cularly to the axis of the body ; it is to this that the 
muscles for moving the tail are attached. 
HaAnng shoAvn above hoAV the frameAvork of the 
