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Henry Gray (1825–1861).  Anatomy of the Human Body.  1918.
 
articular surface of the sternum, revolving, with a sliding movement, around an axis drawn nearly vertically through the sternum; in the circumduction of the shoulder, which is compounded of these two movements, the clavicle revolves upon the articular disk and the latter, with the clavicle, rolls upon the sternum.  1 Elevation of the shoulder is limited principally by the costoclavicular ligament; depression, by the interclavicular ligament and articular disk. The muscles which raise the shoulder are the upper fibers of the Trapezius, the Levator scapulæ, and the clavicular head of the Sternocleidomastoideus, assisted to a certain extent by the Rhomboidei, which pull the vertebral border of the scapula backward and upward and so raise the shoulder. The depression of the shoulder is principally effected by gravity assisted by the Subclavius, Pectoralis minor and lower fibers of the Trapezius. The shoulder is drawn backward by the Rhomboidei and the middle and lower fibers of the Trapezius, and forward by the Serratus anterior and Pectoralis minor.
 
6b. Acromioclavicular Articulation
 
  
(Articulatio Acromioclavicularis; Scapuloclavicular Articulation) (Fig. 326)


The acromioclavicular articulation is an arthrodial joint between the acromial end of the clavicle and the medial margin of the acromion of the scapula. Its ligaments are:
The Articular Capsule. The Articular Disk.
The Superior Acromioclavicular. The Coracoclavicular {Trapezoid and Conoid.
The Inferior Acromioclavicular.

The Articular Capsule (capsula articularis; capsular ligament).—The articular capsule completely surrounds the articular margins, and is strengthened above and below by the superior and inferior acromioclavicular ligaments.

The Superior Acromioclavicular Ligament (ligamentum acromioclaviculare).—This ligament is a quadrilateral band, covering the superior part of the articulation, and extending between the upper part of the acromial end of the clavicle and the adjoining part of the upper surface of the acromion. It is composed of parallel fibers, which interlace with the aponeuroses of the Trapezius and Deltoideus; below, it is in contact with the articular disk when this is present.

The Inferior Acromioclavicular Ligament.—This ligament is somewhat thinner than the preceding; it covers the under part of the articulation, and is attached to the adjoining surfaces of the two bones. It is in relation, above, in rare cases with the articular disk; below, with the tendon of the Supraspinatus.

The Articular Disk (discus articularis).—The articular disk is frequently absent in this articulation. When present, it generally only partially separates the articular surfaces, and occupies the upper part of the articulation. More rarely, it completely divides the joint into two cavities.

The Synovial Membrane.—There is usually only one synovial membrane in this articulation, but when a complete articular disk is present, there are two.

The Coracoclavicular Ligament (ligamentum coracoclaviculare) (Fig. 326).—This ligament serves to connect the clavicle with the coracoid process of the scapula. It does not properly belong to this articulation, but is usually described with it, since it forms a most efficient means of retaining the clavicle in contact with the acromion. It consists of two fasciculi, called the trapezoid and conoid ligaments.
  The Trapezoid Ligament (ligamentum trapezoideum), the anterior and lateral fasciculus, is broad, thin, and quadrilateral: it is placed obliquely between the coracoid process and the clavicle. It is attached, below, to the upper surface of the coracoid process; above, to the oblique ridge on the under surface of the clavicle. Its anterior border is free; its posterior border is joined with the conoid ligament, the two forming, by their junction, an angle projecting backward.
  The Conoid Ligament (ligamentum conoideum), the posterior and medial fasciculus, is a dense band of fibers, conical in form, with its base directed upward. It is
Note 1.  Humphry, On the Human Skeleton, page 402. [back]

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