Part 11

=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.

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. 5a, Its fan-shaped expansion at shoulder-joint laid back. 6, Pectoralis tertius. 7, The coracoid. 8, Biceps. 8a, Its long head. 8b, 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. 28a, Flexor brevis pollicis. 29a, 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).