Trochanteric fossa. 2, Oval articular head at proximal end. 3,
Shaft. 4, Distal end showing articular condyles. 5, Trochanter. 6,
Trochlea for ulna. 7, Trochlea for radius. 8, Depression or fossa.
_H._ Section through the median plane of the humerus showing the
delicate cross partitions illustrating provisions made for bones
provided with air-sac extensions.
]
_Description._—The lumbo-sacral region consists of fourteen vertebræ
which are distinct in the body of the newly hatched chick, but which
become fused soon after hatching. With these vertebral segments there
are fused the last dorsal and first coccygeal vertebral segments. This
fusion is so complete that the segments are indicated only by the
intervertebral foramina on the sides through which the spinal nerves
pass, and by transverse markings on the inferior surface of the bodies.
The lumbo-sacral vertebræ, called the sacrum, and the ilia are fused.
The dorsal spines of the vertebral segments are indicated only in the
anterior portion where they are fused, forming a plate. There are no
prominent ventral spines.
=The Coccygeal Vertebræ= (Fig. 4, No. 27). _Location._—The coccygeal or
caudal vertebræ, or vertebræ coccygeæ, constitute the bones of the tail.
_Description._—There are seven coccygeal vertebræ. The last segment,
shaped like a plough share and therefore called the pygostyle, is the
largest and is supposed to have been formed by the fusion of several
original distinct segments. It supports the coccygeal oil gland and the
row of rudder feathers, or rectrices, which are arranged fan-wise.
All of the coccygeal vertebræ except the first are freely movable, thus
allowing the tail to be used as a rudder during flight. The lateral
spines are long and well developed, and the superior spines are
bifurcated, thus giving increased surface for muscular attachment. The
first coccygeal segment is fused with the last lumbo-sacral vertebra.
THE THORAX
The dorsal vertebræ superiorly, the ribs laterally, and the sternum, or
breast-bone inferiorly, form the skeleton of a large cavity called the
thorax. The dorsal vertebræ have been described.
=The Ribs= (Fig. 4, No. 32; Fig. 10, _A_ and _B_). _Location._—The ribs
form the lateral bony wall of the thorax, articulating superiorly with
the dorsal vertebræ.
_Description._—The ribs are arranged in order of length, the ultimate
rib being the longest. From anterior to posterior, they approach more
nearly a horizontal position. The ribs are divided into the true and the
false. The _true ribs_ articulate with the sternum. The _false ribs_ do
not touch the sternum; they are floating. The true ribs are composed of
two parts, a vertebral, or dorsal, and a sternal, or ventral. The
vertebral part, or _extremitas vertebralis_, is provided with an
articular head, or _caput costæ_; a neck, or _collum costæ_; and an
articular tubercle, or _tuberculum costæ_. The head and tubercle
articulate with the dorsal vertebra. Below the head of each rib is a
_pneumatic foramen_.
The distal extremity of the dorsal section of the rib articulates with
the proximal end of the sternal section by a diarthrodial articulation.
The articulations of the true ribs with the sternum is diarthrodial and
each articulate by two small ridges with a double sternal facet. The
first, the second, and the seventh ribs are floating, or false ribs. The
first rib articulates with the quadrate part of the last cervical
vertebra and also with the first dorsal vertebra. The seventh, the last
rib, articulates with the under side of the anterior alar part of the
ilium. This rib is situated similarly to the true ribs; but, instead of
articulating directly with the sternum, the lower end lies against the
sternal segment of the rib just anterior to it.
From the posterior edge of the second, the third, the fourth, and the
fifth ribs, and near the middle of the dorsal segment, are flat,
uncinate, bony processes which project upward and backward, overlying in
each case, the succeeding rib and giving greater surface for muscular
attachments and greater stability to the thorax.
=The Sternum= (Fig. 4, No. 40; Fig. 10, No. _A_, 9). _Location._—The
sternum, or breast-bone forms the inferior portion, or floor of the
thoracic cavity.
_Description._—The sternum is a quadrilateral, curved plate with
processes projecting from each angle and from the middle of the anterior
and posterior borders. The posterior medial projection, or
_metasternum_, is the longest, and has a tall, plate-like ridge—the
_sternal crest_, _crista sterni_—running along its ventral surface. The
crest serves the important function of increasing the bony area for the
attachment of the powerful muscles which move the wings. The anterior
medial projection, or _rostrum_, is short, and pierced at its root by an
opening from which extend two elongated, saddle-shaped depressions into
which the end of the coracoid bones are received.
The plate-like process of bone, the _posterior lateral process_, which
projects from the caudal angles of the sternum soon divides into two
parts. The shorter of these, the _oblique process_, broadens toward its
free end and covers the sternal segments of the last two ribs. The sides
of the sternum are thus provided with an external and an internal
process forming an _external_ and an _internal_ notch. These notches are
bridged over by a broad ligament, to which the muscles are attached. In
poor flyers, as the domestic fowl, these notches are large. The
posterior end of the sternum is called the _xiphoid process_ or
_processus xiphoideus_. Anteriorly the sternum is provided with lateral
external processes, the _costal processes_. The lateral borders of the
sternum are pitted by four depressions into which the sternal segments
of the ribs are received. The dorsal, or inner surface of the bone is
pierced by openings by which the air-sacs communicate with the interior.
THE APPENDICULAR SKELETON
The appendicular skeleton consists of the shoulder girdle, the fore
limb, the pelvic girdle, or hip bone, and the hind limb. The shoulder
girdle consists of the scapula, the coracoid, and the clavicle. The fore
limb consists of the arm, forearm, and the hand. The arm consists of the
humerus, the forearm of the radius and the ulna; and the hand consists
of the carpus, the metacarpus, and the phalanges. The pelvic girdle
consists of the ilium, the ischium, and the pubis. The hind limb
consists of the thigh, the leg, and the foot. The thigh consists of the
femur, and the leg consists of the tibia and the fibula. The foot
consists of the metatarsus and the phalanges.
THE SHOULDER GIRDLE
The shoulder girdle consists of the scapula, the clavicle and the
coracoid.
=The Scapula.= _Location._—The scapula (Fig. 11, _A_, _B_) lies on the
outer and superior rib surface, extending parallel with the dorsal
vertebræ.
_Description._—The scapula is a thin, sword-like bone, becoming thicker
as it approaches the shoulder-joint. The scapula expands and becomes
thin near the free end, which reaches nearly to the antero-lateral
portion of the ilium (Fig. 4, No. 24). The scapula articulates with the
coracoid. A _pneumatic foramen_ is located at the base of the acromion
process. The anterior part of the scapula is provided with an articular
head and is provided with an inner process, called the _processus
furcularis_, which lies near the furcula and coracoid. An outer stronger
_processus humeralis_ forms the posterior half of the _glenoid cavity_,
or _cavitas glenoidalis_, in which the humerus articulates and the
processus coracoideus.
=The Clavicle.= _Location._—The clavicles, commonly known as the wish
bone, are located in the anterior chest region.
_Description._—The clavicles are long, slender bones uniting below in
the _hypocledium_, a laterally flattened process. They are joined to the
upper end of the coracoid by fibrous cartilage. The hypocledium is
joined to the anterior point of the sternum by the claviculosternal
ligament. The clavicles, as united by the hypocledium, form a v-shaped
structure called the furculum, or, popularly, the wish bone.
The forks play the part of an elastic spring, whose office it is to
prevent the wings from coming toward each other during contraction of
the depressor muscles. The conformation of this bone is, therefore, like
the sternum, related to the extent and power of flight; and for this
reason it is that, in swift flyers, the two branches of the furculum are
thick, solid, widely separated, and curved like a U; while in those that
fly heavily and with difficulty, these branches are thin and weak, and
join at an acute angle. The latter formation greatly diminishes its
strength, and lessens, in a singular manner, the reactionary power of
the bony arch it represents.
=The Coracoid.= _Location._—The coracoid is located just back of the
clavicle and at the side of the entrance of the thoracic cavity. It is
the strongest bone of the shoulder girdle, extending upward, outward,
and forward. It articulates inferiorly with the sternum and superiorly
with the humerus and the scapula, and is attached to the superior end of
the furcular limb by a fibrous cartilage.
_Description._—It is thinnest in the center or shaft and broadens toward
the inferior extremity. The upper hook-like part of the coracoid forms
the fore part of the glenoid cavity, and together with the scapula and
furcula form the foramen triosseum through which passes the tendon of
the elevator muscle of the wing. The upper end flattens out into three
tuberosities, the tuberositas furcularis which is thick and to which
attaches the limb of the furcula, the tuberositas scapularis which
unites to the scapula, and the tuberositas humeralis which lies between
these and articulates with the humerus.
THE FORE LIMB
The bones of the fore limb are humerus, ulna, radius, carpus,
metacarpus, and phalanges.
=The Humerus.= _Location._—The humerus constitutes the arm, which, when
at rest, lies parallel to the dorsal vertebræ. It articulates superiorly
with the glenoid cavity, a shallow ball-and-socket joint, formed by the
scapula and the coracoid; and inferiorly with the ulna and radius.
_Description._—The proximal extremity of the humerus is provided with a
trochanter (Fig. 11, _G_, No. 5) and a large oval head or caput humeri,
which articulates in the glenoid cavity. The head is an elongate,
semi-oval convexity, with the long axis transverse from the radial to
the ulnar side and with the ends continued into upper and lower crests.
The upper crest of the head of the humerus is on the radial side and the
lower crest on the under side. Under this latter crest there is a
_pneumatic fossa_ (Fig. 11, _F_, No. 1), at the upper end of which there
is an opening into the bone, the _pneumatic foramen_, which brings the
air-sac into communication with the air space of the bone. The shaft, or
corpus humeris, is irregularly cylindrical and slightly S-shaped.
The proximal part of the shaft, which is expanded on the palmar side, is
concave across and convex lengthwise. The distal part is slightly
flattened. The shaft of the humerus is almost cylindrical.
The distal extremity of the humerus is provided with two articular
condyles, one of which articulates with the ulna and the other with the
radius. On the radial side of the palmar surface there is a ridge; and
on the ulnar side of the same surface there is a second ridge diverging
to the opposite tuberosity. The radial surface is a narrow, subelongate
convexity, extending from the middle, approximately, of the palmar
surface, obliquely to the lower part of the radial tuberosity. The two
_articular convexities_, or _trochlea_, at the distal end of the humerus
are bent toward the palmar aspect, the _anconal aspect_ is the side on
which the elbow is situated. The inner convexity is the larger and
articulates with the ulna. To the outside is the _processus cubitalis
humeri_. The outer articulates with the radius and is so arranged that
the radius makes a greater flexion than the ulna. At the lower end of
the humerus there is a depression which receives the anconeus of the
ulna during flexion and extension of the forearm. On the shoulder- and
elbow-joint are found grooves over which the tendons glide, at which
places sheaths are provided. This arrangement also aids in keeping the
capsular ligament in place.
=The Ulna.= _Location._—The ulna, larger than the radius, is bent and
articulates with the radius only at the ends. The two bones are bound
together by a ligamentous band. It also articulates superiorly with the
distal end of the humerus, and inferiorly with the carpus. When the wing
is folded the radius is superior and a trifle to the inner side of the
ulna.
_Description._—The proximal end is most expanded, and is obliquely
truncate for the articular excavation adapted to the ulnar tubercle of
the humerus. A short angular process behind the cavity represents the
_olecranon_, which is the _processus olecranalis coracoideus ulnæ_ to
which the ligamentum capsulare cubiti attaches. On the inner side of the
head is the internal tubercle of the ulna and on the external side the
external tubercle of the ulna. An excavation is noted on the radial side
of the proximal end for the lateral articulation of the head of the
radius. On the upper side near the articular part is located the
_sigmoid cavity_.
The shaft, or corpus ulnæ, decreases in size near the distal end. It is
slightly curved, flattened laterally with an internal and an external
ridge.
The distal end of the ulna is slightly expanded into a _trochlea_ which
is sharply convex and articulates with two free carpal bones, the
scapho-lunar, or os carpi radiale, and the cuneiform, or os carpi
ulnare. The scapho-lunar is placed on the radial side, and the
carpiulnare on the ulnar side. The distal extremity of the ulna is
provided with a _styloid process_ and on the dorsal side with a
_tubercle_.
=The Radius.= _Location._—The radius lies beside the ulna with which it
articulates at each extremity. At the inferior extremity the
articulation is rotary. It also articulates superiorly with the humerus
and inferiorly with the os carpi radiale.
_Description._—The radius, cylindrical in shape, is more slender than
the ulna.
The proximal end is expanded, subelliptical, with a concavity for the
oblique tubercle and a thickened convex border for articulation with the
ulna. This end is provided with the _tuberositas radii_.
The shaft, or corpus radii, is slender, subcompressed, and has a slight
bend upward from the ulna. A nutrient foramen occurs in this shaft.
The distal end is expanded and rather flattened with two grooves on the
anconal side for passage of tendons. For articulation with the
scapho-lunar the radius is provided with a terminal _transverse
convexity_ produced palmad, which also articulates with the ulna
laterally. There is a tuberosity on the radial side of the expansion and
inferiorly the _inferior tuberculum ossis carpi radialis_ and superiorly
a _superior tuberculum ossis carpi radialis_.
=The Hand.=—The hand is made up of the carpus, the metacarpus, and the
phalanges.
The bones of the hand are so arranged as to allow abduction and
adduction, or flexion in the ulno-radial plane, movements which are
necessary in the outspreading and folding of the wing. Thus the hand of
the fowl moves in a state of pronation, without the power of rotation.
The carpal bones are so placed between the anterior arm and metacarpus
as to reduce the abduction which is necessary to hold and extend the
wing, so that the hand or wing be in a fixed position.
=The Carpus.=—The carpus in the domestic fowl is represented by two
bones, ossa carpi, called the _scapho-lunar_, or _os carpi radiale_, and
the _cuneiform_, or _os carpi ulnare_. The scapho-lunar is the smaller
and is located between the radius and metacarpus. The cuneiform is the
larger and is located between the ulna, the radius, and the metacarpus.
The cuneiform is somewhat anvil-like in shape, being provided with a
body and two prongs.
=The Metacarpus.=—The metacarpal bones, or ossa metacarpi, two in
number, are separated at their middle portion, and consolidated at their
extremities. The upper proximal base of the metacarpus is provided with
a tubercle, the tuberculum muscularis, and externally the tuberculum
ulnare ossis metacarpi. The distal end of the metacarpal bone is
provided with a tuberculum articulare.
=The Phalanges.=—The first three fingers only are represented, and these
are rudimentary.
The first finger called the pollex or thumb, consists of but one joint.
It is located on the proximal and outer end of the metacarpal bone. It
has on its proximal end a tubercle, the tuberculum articulare.
The second finger, the best developed, consists of two phalanxes. These
are the main bones extending from the metacarpus. Each articular end is
provided with a _tuberculum articulare_.
The third finger, small, cylindrical in shape, is located at the distal
and inner side of the metacarpal bone.
=THE PELVIC GIRDLE= (Fig. 4, No. 25; Fig. 5, Part II, 6)
The pelvic girdle is made up of three bones as follows: the ilium, the
ischium, and the pubis, all of which are fused in adult life. They are
separate in the baby chick (Fig. 5, Part II, 6). The pelvis together
with the lumbo-sacral vertebræ forms a thin, irregular, shell-like
structure extending superiorly from the tail to the thoracic region. The
sacrum is broad posteriorly and together with the ilium forms the pelvic
roof. The ilium and ischium are its lateral walls.
The top surface of the pelvis shows the _fovea ilio-lumbalis dorsalis_,
which is bounded mesially by the crista ilii. Between it and the spina
lumbalis there is a broad furrow, the bottom of which is formed by the
dorsal surface of the lumbar vertebræ. The _sulcus ilio-lumbalis
dorsalis_ is formed by the rims of the ilia, so that a ridge is
observable. The _cavum ilio-lumbale dorsale_ is formed by the iliac rims
on either side. Anteriorly is the _canalis ilio-lumbalis_, which is
formed by the ilium and the lumbar vertebral spines. It is located
longitudinally to the vertebræ. The anterior opening of this canal is
the larger. Posterior to the _acetabulum_ is the _post-acetabular_
ridge.
The under part of the pelvis presents three distinct regions. The cavity
is divided into the _fovea lumbalis_, or anterior part, the _fovea
ischiadica_, or mesial part, and the _fovea pudendalis_, or posterior
part. Posterior to these is the region called the _planum coccygeum_.
The fovea lumbalis contains the anterior lobe of the kidney, and is
circumscribed anteriorly by the last rib-carrying vertebra, and
posteriorly by the transverse process of the last lumbar vertebra.
In the fovea ischiadica which follows, lie the nerve plexus ischiadicus
and the middle lobe of the kidney. Its posterior boundary is the linea
arcuata. The linea arcuata is a line drawn from the acetabulum of the
one side to the acetabulum of the other side.
The fovea pudendalis contains the posterior lobe of the kidney. The
posterior boundary is the anterior border of the first coccygeal
vertebra. It gives passage to the nerve plexus pudendo-hemorrhoidalis.
The ilium, the ischium, and the pubis join to form the cotyloid cavity,
or acetabulum, in which articulates the head of the femur. The floor of
the cavity is perforated by a relatively large round foramen.
=The Ilium.= _Location._—The ilium, together with the lumbo-sacral
vertebræ, forms the roof of the pelvic cavity. It articulates at its
inner border with the lumbo-sacral vertebræ, postero-laterally with the
ischium and at the cotyloid cavity with the pubis.
_Description._—The ilium is remarkable for its development in the long
axis of the vertebral column. It is long and narrow; and mesially, where
it is thickest it forms the upper wall of the acetabulum. Anterior to
the acetabulum it is outwardly concave, and posterior to the acetabulum
it is convex. The ilium fuses with the last dorsal vertebra and with the
lumbo-sacral vertebræ and is excavated on its internal face. This
surface is irregular and lodges the kidneys. This inner margin of the
renal part enters with the square extensions of the posterior excavation
passing into the posterior iliac spine. The external margin is the
extension of the crista transversa and forms the _processus
ischiadicus_. Posteriorward the renal part of the ilium joins the
ischium.
The ilia converge at the summits of the anterior sacral spines forming
the _ilio-lumbar_ spines.
The ilium is joined to the square extensions of the last sacral vertebra
by the _symphysis ilio-sacralis_, to the larger part of the lumbar
vertebræ by the _sutura ilio-lumbalis_, and to the transverse processes
of the last sacral vertebræ by the _symphysis ilio-sacri_.
=The Ischium.= _Location._—The ischium is located in the
postero-inferior part of the pelvis. It joins superiorly with the ilium,
and inferiorly with the pubis.
_Description._—The ischium is smaller than the ilium and is a flattened,
triangular-shaped bone, thickest where it forms the posterior part of
the acetabulum, becoming thinner and broader as it extends backward.
Posteriorly it forms the caudal extension. The inferior border is turned
slightly outward and is fused with the pubis. Between these bones there
is located the large oval _ischiadic foramen_, through which passes the
ischiadic nerve. This bone aids the ilium in the formation of the
obturator foramen through which passes the tendon of the internal
obturator muscle. The lower part of the ischium which separates the
ischiadic foramen from the obturator foramen is called the _ramus
ascendens ossis ischii_.
=The Pubis.= _Location._—The pubis is located along the inferior margin
of the ischium and extends further back than the posterior border of the
ischium.
_Description._—The pubis is a long, slender, rib-like bone. It forms the
lower and front portion of the acetabulum. The ischiadic foramen formed
by the ischium and pubis is single and nearly circular in fowls, double
in pigeons, and in geese and ducks it is elongate.
THE HIND LIMB (Fig. 4, Nos. 35, 47, 48, 49, 50, 51, 52, and 53; Fig. 12)
The pelvic, or hind, limb supports the body. The bones of each leg are
the femur, which constitutes the thigh, the tibia and the fibula, which
represents the leg, and the metatarsus and the phalanges, which form the
foot.
=The Femur= (Fig. 12, _A_ and _B_). _Location._—The femur, or os
femoris, the first bone of the hind extremity, extends obliquely
downward and forward, articulating with the acetabulum above and the
tibia, the fibula, and the patella below.
_Description._—The femur, one of the largest, thickest, and strongest
bones of the body, belongs to the class of cylindrical bones, and
presents for examination a shaft and two extremities.
The superior, or proximal extremity, is provided with a head, caput
femoris; the neck, collum femoris; and the trochanter. The head is
relatively small, and is marked by a depression above for the round
ligament which fills the cavity in the acetabular wall. Its axis is
nearly at right angles with the shaft. A neck joins it to the body at
the proximal end. External to the head of the femur is the _trochanter_.
The trochanter presents an outer convexity over which the tendon of the
gluteus maximus extends to become inserted below. The _trochanteric
ridge_, which is opposite the articular head, presents an outer
flattened surface which possesses impressions for muscular attachments.
The _trochanteric fossa_, or fossa trochanterica, is shallow.
The _shaft_, or _corpus femoris_, is shorter than the tibia, is in
general cylindrical, bent forward, and the lower half is flattened and
expanded transversely. A nutrient foramen is located in the median
portion of the shaft. The shaft shows muscular linear ridges.