_trochlea_ in front and two _condyles_ behind, one internal and one
external. The condyles are separated by the _intercondyloid fossa_, or
_fossa intercondyloidea_, which is marked with pits for the attachment
of ligaments; and above this is the _epitrochlear fossa_.
[Illustration:
FIG. 12.—Bones of the hind extremity.
_A._ Posterior view of femur.
_B._ Anterior view. 1, Shaft. 2, Proximal extremity. 3, Distal
extremity. 4, Articular head. 5, Trochanter major. 6, Shallow
trochanteric fossa. 7, Convexity over which the tendon of the
gluteus maximus glides. 8, External condyle. 9, Internal condyle.
10, Nutrient foramen. 11, Intercondyloid fossa. 12, Muscular linear
ridges. 13, Epitrochlear fossa.
_C._ Internal view of tibia.
_D._ External view. 1, Shaft. 2, Articular head. 3, Distal end. 4, The
rotular process. 5, The fibular ridge. 6, External condyle. 7,
Internal condyle. 8, Intercondyloid space. 9, Nutrient foramen.
_E._ Fibula, lateral view. 1, Articular head. 2, Its attenuated
portion.
_F._ Posterior view of metatarsus. 1, Trochlea for inner or second
digit. 2, Trochlea for middle or third toe. 3, Trochlea for outer
digit. 4, Bony core for spur. 5, Bony canal for tendons. 6, Groove
for tendons. 7, Fossa intercondyloidea.
]
The _inner condyle_ begins anteriorly as a ridge, and expands into a
convexity which attains its greatest breadth posteriorly where it
becomes more flattened. The inner side of the inner condyle is flattened
and is provided with a tuberosity at its mid-part and a second just
above the posterior part of the condyle.
The _outer condyle_ is formed in the same manner as the inner condyle.
It is indented at its broad, lower end by an _angular groove_, which,
winding divides the posterior part of the condyle into two convexities.
The more external convex ridge and the groove dividing it from the outer
condyle are adapted to the head of the fibula. There is in this part a
_fibular ridge_ and above this ridge a tuberosity.
=The Tibia.= _Location._—The tibia (Fig. 12, _D_ and _C_) extends
obliquely downward and backward from the knee-joint to the hock. It
articulates above with the femur and, by its procnemial process with the
patella, below with the metatarsus, and laterally with the fibula.
_Description._—The tibia is the longest bone in the posterior limb, and
possesses a shaft and two extremities. It is largest at the proximal end
and presents three faces.
The proximal extremity presents a semi-oval articular surface, not quite
at right angles with the shaft, which articulates with the condyles of
the femur. The margin is raised toward the anterior of the bone. The
_head of the tibia_, or _caput tibiæ_, extends into a rotular process
which extends transversely, and is truncate. From the anterior of this
process there descends two vertical ridges; one near the angle of the
rotular process, the _procnemial ridge_; the other from the outer
fibular angle, the _ectocnemial ridge_. On the outer side of the
intercondylar tuberosity there is a surface for the ligamentous union
with the head of the fibula; and a short distance below this there is a
vertical ridge for the close attachment, almost a fusion, with the
fibula, called the _fibular ridge_.
The _shaft_, or _corpus tibiæ_ is straight and the upper two-thirds
subtrihedral; the lower third oval. A _nutrient foramen_ occurs near the
upper postero-internal portion of the middle third of the bone.
The distal extremity is much smaller than the proximal one; it is
quadrangular in form. The expanded inferior end of the tibia forms two
articular condyles above which posteriorly there is the _epicondyloid
fossa_. The inner condyle, the larger, has a groove near the lower end
of the anterior part of the shaft, which deepens toward the
intercondyloid space. This _intercondyloid fossa_ in young birds is
covered by a strong ligament, which in older birds, becomes ossified. On
the lateral side of each condyle, there is a depression for the
attachment of ligaments.
=The Patella.= _Location._—The patella, or knee-cap, thin and wide,
articulates with the procnemial process of the tibia, and with the deep
trochlea of the distal end of the femur.
_Description._—The patella is irregular in shape with three faces and
three borders. The posterior surface is articular. The other two
surfaces are rough for tendinous attachment. The patellar ligaments in
old birds may become ossified.
In order to turn the foot in and out, the tibia not only turns around
the inner condyle of the femur, but also around the patella, so that the
posterior surface turns outward and thus turns outward the metatarsus
and all the toes.
=The Fibula.= _Location._—The fibula lies at the outer border of the
tibia. It articulates superiorly with the outer condyle of the femur,
and laterally with the tibia.
_Description._—The fibula is rudimentary; it is largest superiorly and
tapers to a slender point. The head is compressed laterally, and
furnishes an upper and an inner articular surface.
=The Tarsus.=—There exist, during fetal development of the chick, two
rows of tarsal bones which later become fused. The upper row fuses with
the tibia and the lower with the metatarsus. Therefore, in the adult,
there is no tarsus.
=The Metatarsus.= _Location._—The metatarsal bone extends downward and
forward. In birds it consists of one bone, which articulates superiorly
with the inferior extremity of the tibia. On the distal end it has a
threefold trochlear arrangement which articulates with the three
principal digits.
_Description._—The proximal extremity posteriorly has a process which
may be considered as a consolidation of originally separate metatarsal
bones. The process at the supero-posterior part of the metatarsus is
called the _hypotarsus_ of the _tarso-metatarsus_, through which extends
a canal called the _hypotarsal canal_, and which gives passage to flexor
tendons.
The proximal end of the metatarsus is ossified from one center of
ossification forming an epiphysis which caps the ends of the three
original metatarsal bones that coalesce, first with one another, then
with the epiphysis, thus forming a single compound bone. Above and just
to the inside of the metatarsus there may occur a small bone which is
imbedded in ligaments and articulates with the inner proximal surface of
the metatarsus. This has been called by Gadow a _sesamoid bone_.
The shaft shows _tendonal grooves_ which are best marked on the
posterior surface. The shaft is rounded at the sides and flattened on
the anterior and posterior surfaces. At the juncture of the middle and
inferior thirds of the metatarsus there is a conical process turned
slightly backward, which serves as a base for the _spur_. The spur is a
horny structure.
At the distal extremity occurs the threefold trochlear arrangement
mentioned above, which incloses the fossa intercondyloidea. The inner
trochlea is the broadest, and the outer the narrowest. The inner
trochlea articulates with the proximal end of the second, the middle
with the third, and the outer with the fourth toe.
=The Phalanges.= _Location._—Most domestic fowls are provided with four
digits, or toes; the Houdan and Dorking are provided with five. In fowls
with four toes the three principal toes, the second, the third, and the
fourth, are directed forward, and the first, or hallux, is directed
backward.
_Description._—The last phalanx of each toe, called the ungual phalanx,
is slightly curved downward, is pointed anteriorly, like the claw of the
cat or dog, and is covered with a horny sheath. The articular ends of
the joints of the phalanges are enlarged. The base of the basal phalanx
has two enlargements, the superior-inferior tubercles, or tuberculum
superius et inferius, between which is located the fossa articularis
transversa. Laterally the head has two condyles, condyli laterales,
which are divided by the sulcus longitudinalis. The bodies of the
phalanges vary in form; they are superiorly rounded, but inferiorly
rounded, flat, or even somewhat concave. The distal extremity has an
articular trochlea.
The _first toe_, or digit, called the _great toe_, or _hallux_, is
composed of three phalanges, or segments. The first segment, or basal
phalanx is considered a rudimentary metacarpal bone; it is attached by a
fibrous cartilaginous tissue to the inner posterior surface of the
inferior extremity of the metacarpal bone just below the spur.
The _second toe_, likewise composed of three phalanges, is directed
forward. It articulates with the inner trochlea located on the inferior
metacarpal bone.
The _third toe_, made up of four phalanges, is the middle of the three
forward toes. It articulates with the middle trochlea of the inferior
extremity of the metacarpal bone.
The _fourth toe_, is composed of five phalanges; it is, however, of
approximately the same length as the third, the segments being shorter.
The fourth or outer toe articulates with the outer trochlea of the
distal extremity of the metacarpal bone.
ARTHROLOGY
=Kinds of Joints.=—Joints may be movable, immovable, or mixed. In
_movable_, or _true joints_ the articular surface of each bone is
covered by cartilage. The bones are held together by ligaments, the
capsular one often surrounding the joint and enclosing the synovial
membrane. In some joints there is a pad of fibrous cartilage interposed
between the two articular cartilages. Such a pad, called a _meniscus_,
adds to the elasticity and the free movement of the joint. Movable
joints form the most numerous class; they are for the most part found in
the limbs.
In an _immovable joint_ there is only a thin layer of fibrous or
cartilaginous material interposed between the bones. The fibrous layer
of the periosteum of both bones unite to cover the connecting material
and becomes attached to the same, thus serving as a ligament. If the
connecting material is fibrous, the joint is called a _suture_; if
cartilaginous, a _synchondrosis_. These joints are found in the skull
and in the pelvis.
The term _mixed_ is used with reference, not to the motion in joints,
but to their structure, which partakes of the nature of both the movable
and immovable. The bones are firmly joined by a strong interposed pad of
fibrous cartilage to which also is adherent the ligaments of the joint.
There are no capsular ligaments; the cartilaginous pad or disc is softer
toward its center, where occasionally there may be one, or even two,
narrow cavities. Authorities differ as to whether such cavities are
lined by synovial membrane or not. Since there are really no frictional
surfaces in such a joint, motion depends upon the flexibility of the
disc. The joints between the vertebral centra afford the best
illustration of the mixed class.
=Movement of Joints.=—The movements admissible in joints may be divided
into four kinds: gliding, angular movement, circumduction, and rotation.
These movements are often, however, more or less combined in the various
joints. It is seldom that there occurs only one kind of motion in any
particular joint.
_Gliding movement_ is the most simple kind of motion that can take place
in a joint, one surface gliding or moving over another without any
angular or rotary movement.
_Angular movement_ occurs only between the long bones. By it the angle
between the two bones is increased or diminished. It may take place in
four directions: forward and backward, consisting of flexion and
extension; or inward and outward from the medial line of the body,
consisting of adduction and abduction. Abduction of a limb is movement
away from the medial line of the body. Adduction of a limb is movement
toward the medial line of the body.
_Circumduction_ is that limited degree of motion which takes place
between the head of a bone and its articular cavity, whilst the
extremity and sides of the limb are made to circumscribe a conical
space, the base of which corresponds with the inferior extremity of the
limb, the apex with the articular cavity; this kind of motion is best
seen in the shoulder- and hip-joint.
_Rotation_ is the movement of a bone upon an axis, which is the axis of
the pivot on which the bone turns, as in the articulation between the
atlas and axis, when the odontoid process serves as a pivot around which
the atlas turns; or else is the axis of a pivotlike process which turns
within a ring, as in the rotation of the radius upon the humerus.
_Pronation_ is a form of rotation in which the inferior extremity of the
radius passes before the ulna, and thus causes the hand to execute a
kind of rotation from without inward.
_Supination_ is a form of rotation in which the movement of the forearm
and hand are carried outward so that the anterior surface of the latter
becomes superior.
=The Ligamentous Structure.=—Ligaments are dense, fibrous, connecting
structures. They are made up principally of white fibrous tissue and
exist in all true joints.
There are four kinds of ligaments associated with true joints:
The first kind, the _capsular ligament_ which encloses all true joints,
is thin and consists of interlaced fibers attached to the bone at the
edges of the articular cartilages. It either partly or wholly surrounds
the joint, enclosing and protecting a synovial apparatus, which, by
secreting a liquid resembling serum, lubricates the joint to prevent
friction.
The second kind, the binding or _lateral ligaments_, consist of
flattened or rounded cords or bands of fibrous tissue. Such a ligament
extends from one bone to the other, and firmly attached to their
roughened surfaces, holds the bones in place and at the same time allows
the required amount of motion.
The third kind, located between the joints, is called _interosseous
ligament_.
The fourth kind, called the _annular ligament_ binds down and protects
the tendons.
=Ligaments of the Ear[2].=—The concha of the ear is provided with a
superior and an inferior ligament.
Footnote 2:
The classification of Gadow is used.
=Ligaments of the Jaw.=—The articulations of the lower jaw are complex.
The freely movable articulation is between the inferior maxilla and the
quadrate. Less freely movable articulations are formed by the quadrate
with the temporal, the zygomatic and the pterygoid. A lateral ligament
of the jaw, the _articulo-jugale_ extends from the posterior border of
the inner wing of the os articulare of the inferior maxilla (Fig. 8, No.
10, and Fig. 19, No. 15) to the outer border of the os quadrato
jugulare.
A _lateral temporo-maxillary ligament_ extends from the outer surface of
the temporal bone to the outer border of the os articulare of the
inferior maxilla (Fig. 8, No. 11, and Fig. 19, No. 14).
=Ligaments of the Vertebræ.=—In each space between the bodies of the
vertebræ there is a _meniscus intervertebralis_. This meniscus is
analogous to the annulus fibrosus of mammals (Gadow), which, is possibly
formed as a protrusion of the anterior surface of the vertebral body.
The meniscus or disc may develop into a ring-shaped structure, the true
meniscus, or it may develop to different degrees as an extension of the
vertebral body surface, and become, as in the dorsal and lumbar regions,
fused with the vertebral segments, in which case it is called the
annulus fibrosus.
The vertebral disc which is connected with the atlas and which is fused
with that bone, represents the first meniscus, which is called the
_ligamentum transversum atlantis_. This, as well as other ligaments of
the spinal column, may become ossified.
The ligament which is located between those vertebral bodies which face
each other and is inside the joint cavity, is called the _ligamentum
suspensorium corporum vertebralium_. It passes through the central
opening of the meniscus and lies exactly in the long axis of the body of
the vertebra.
The first ligament of the neck is the _ligamentum suspensorium dentis
epistrophei_. The _ligamentum capsulare atlantico-occipitale_ and the
_ligamentum capsulare atlantico-epistrophicum odontoideum_ are two parts
of the joint capsule of the vertebral body. Other ligaments of this part
are the _membranæ obturatoriæ intervertebrales posteriores_, which are
located between the semicircular rims of the neck vertebræ.
The _ligamentum transversum atlantis_ surrounds the occipital condyle.
The _ligamentum nuchæ_ is a thin, membranous, ribbon-like structure
which lies between the muscles of the right and those of the left side
of the middle, and the lower part on the posterior of the neck, and ends
in attachments to the superior spines of the cervical vertebræ.
The _ligamentum elasticum interspinale profundum_ and the _ligamentum
elasticum interspinale superficiale_ and the three last named are the
ligaments which keep the neck of the fowl in the s-shape, without the
action of the muscles.
The _ligamentum capsulare obliquum_ connects the facets of the oblique
processes.
=Ligaments of the Ribs.=—The thick inferior end of the sternal portion
of the true rib has two small articular heads, which articulate with two
depressions in the articular surface of the sternum. This articulation
is held firm by a _capsular ligament_.
The upper end of the sternal rib forms an almost perfect right angle
with the inferior end of the dorsal rib with which it is connected by a
joint provided with a synovial apparatus and a capsular ligament. This
arrangement allows free movement outward and inward and is the main
joint in respiration.
The upper end of the dorsal portion of the rib articulates with the
dorsal vertebra. The joint formed by the articular head with the body of
the vertebra is provided with a capsular ligament. The tubercle of the
rib articulates with the facet on the transverse process of the dorsal
vertebra, and is provided with a transverse ligament, called the
_ligamentum transversum externum_. It is also provided with a capsular
ligament.
The _ligamentum triangulare_ connects each processus uncinatus with the
succeeding rib. This ligament is in the form of a membranous sheet, or
aponeurosis.
=Ligaments of the Sternum= (Fig. 13).—The external and the internal
notches of the sternum are bridged over with a thin membrane which gives
an extensive surface for muscular attachments. The sternal muscles
overlie this portion.
[Illustration:
FIG. 13.—Muscles of the fore extremity. Inside view. 1, Lateral
external process of sternum. 2, Lateral internal process of same. 3,
Ligament of the external notch. 4, Ligament of the internal notch.
5, Pectoralis major. 5_a_, Its fan-shaped expansion at
shoulder-joint laid back. 6, Pectoralis tertius. 7, The coracoid. 8,
Biceps. 8_a_, Its long head. 8_b_, Its short head. 9, Pectoralis
secundus. 10, Rectus abdominis. 11, Teres et infraspinatus. 12,
Deltoid. 13, Capsular ligament. 14, Teres minor. 15,
Coraco-brachialis. 16, Serratus magnus anticus. 17, Extensor
metacarpi radialis longior. 18, Pronator brevis. 19, Flexor carpi
ulnaris. 20, Flexor carpi ulnaris brevior. 21, Flexor digitorum
profundus. 22, Extensor indicis longus. 23, Extensor ossis metacarpi
pollicis. 24, Humerus. 25, Shoulder. 26, Elbow. 27, Carpus. 28,
Section through vertebra. 29, Keel of sternum. 28_a_, Flexor brevis
pollicis. 29_a_, Extensor proprius pollicis. 30, Flexor minimi
digiti brevis. 31, Interosseous palmaris. 32, Interosseous palmaris.
]
The sternum is connected by a fibrous mass with the inferior portion of
the clavicle, or hypocledium (Fig. 57), the _claviculosternal ligament_.
The inferior narrow elongated end of the coracoid forms with the sternum
a true articulation, which is provided with a capsular ligament, the
_ligamentum capsulare_. Capsular ligaments occur at the articulations
between the sternum and ribs.
=Ligaments of the Shoulder-joint= (Fig. 13).—The shoulder-joint is made
up of the scapula, the humerus, and the coracoid. The ends of these
three bones form the _foramen triosseum_ (Fig. 15, No. _A_, 7) through
which passes the tendon of the elevator muscle of the wing.
The furcula, independent of the shoulder-joint or girdle, is attached to
the supero-internal part of the proximal end of the coracoid by fibrous
connective tissue; it is also connected to the other bones of the
shoulder-joint by the _ligamentum coraco-furculare_ and the _ligamentum
furculo-scapulare_.
The _ligamentum coraco-scapulare_ extends from the tuberosity of the
furcula to the coracoid and to the processus furcularis of the scapula.
The _ligamentum coracoido-scapulare externum_ extends between the
external tuberosity of the coracoid, the tuberosity of the scapula, and
the humerus.
The _ligamentum coracoideo-scapulare inferius_ extends from the coracoid
to the inner tubercle of the scapula.
Another long, broad ligament belongs to the episternal apparatus.
The shoulder-joint is provided with a wide, loose, _capsular ligament_
(Fig. 13, No. 13). Attached to the humerus are four other ligaments, of
which three pass from the anterior end of the coracoid and the fourth
from the scapula. The latter are as follows: first, the _supero-anterior
ligamentum humero-coracoideum_, which extends from the small tubercle of
the humerus to the coracoid bone; second, the _antero-inferior
ligamentum humero-coracoideum_, which extends from the humerus to the
coracoid; third, the _ligamentum coraco-humerale_, which extends from
the coracoid to the large tubercle of the humerus; fourth, the
_ligamentum humero-scapulare_ which extends between the processus
humeralis of the scapula and the head of the humerus.
=Ligaments of the Elbow-joint= (Fig. 14).—The elbow-joint is made up of
the ulna, radius and the humerus. The ligaments of the elbow-joint are
as follows: the _ligamentum capsulare cubiti_, or capsular ligament,
which extends from the processus cubitalis of the humerus to the
processus olecranalis coracoideus of the ulna and to the tuberositas
radii of the radius (Fig. 15, No 5).
The _ligamentum laterale cubiti externum_ connects the outer humeral
distal extremity with the head of the radius (Fig. 15, No. 2).
The _ligamentum laterale cubiti internum_ lies between the inner distal
extremity of the humerus and the tuberculum internum of the ulna (Fig.
14, No. 9).
The _ligamentum annulare radii_ originates on the olecranon, surrounds
the head of the radius, and is attached to the tuberculum internum of
the ulna (Fig. 15, No. 3).
The _ligamentum cubiti teres_ extends from the head of the radius to the
upper end of the ulna (Fig. 15, No. 4).
[Illustration:
FIG. 14.—Muscles and ligaments of the arm and forearm of a hen.
_A._ External view. 1, Expansor secundarium. 2, Tensor patagii longus.
3, Tensor patagii brevis. 5, Brachialis anticus. 6, Pronator longus.
7, Supinator brevis. 8, Extensor indicis brevis. 10,
Scapulo-humeralis.
_B._ Internal view. 9, Ligamentum laterale cubiti internum.
]
The _ligamentum transversum_ spreads out between the head of the ulna
and the radius, thus uniting the two bones, and limiting supination
(Fig. 15, No. 1).
=Ligaments of the Carpal Joint.=—The carpal joint is made up of the
ulna, radius, the two carpal bones and the metacarpus.
There are two strong _ligamenta obliqua carpi ulnaris_ which extend from
the processus styloideus of the ulna to the tuberculum posterius carpi
ulnaris of the os carpi ulnaris.
The _ligamentum posticum ulnare carpi ulnaris_ extends from the
processus styloideus of the ulna to the os carpi ulnaris.
[Illustration:
FIG. 15.—Ligaments of the arm and forearm of a hen.
_A._ The scapulo-coraco-humeral articulation. 1, Proximal end of the
humerus. 2, Articular head of humerus. 3, The coracoid. 4, Proximal
end of the clavicle. 5, Tendon of pectoralis tertius. 6, Tendon of
pectoralis secundus. 7, Opening or foramen triossium through which
the tendon of the elevator of the wing passes. (Pectoralis
secundus.) 8, Broken end of scapula.