STERNO-COSTO CLAVICULAR JOINT 



249 



inch (6 mm.) deep with the concavity upward, its upper border tapering to a 

 narrow, almost sharp edge. It is connected with the posterior superior angle of 

 the sternal extremity of each clavicle, and with the fibres which weld the inter- 

 articular cartilage to the clavicle; and then passes across from clavicle to clavicle 

 along the posterior aspect of the upper border of the manubrium sterni. The 

 lowest fibres are attached to the sternum, and join the posterior fibres of the 

 capsule of each joint. In the middle line, between the ligament and the sternum, 

 there is an aperture for the passage of a small artery and vein. 



In addition to the interclavicular ligament Mr. Carwardine ("Journal of Anatomy and 

 Physiology," vol. 7, new series, p. 232) has described a special band of the upper portion of the 

 sterno-clavicular capsule which he proposes to name the 'suprasternal Ugament.' It descends 

 from the upper border of the sternal end of the clavicle to the upper border of the sternum, and 

 is of special importance as it encloses the suprasternal bones, when these rudiments are present. 



The costo -clavicular or rhomboid ligament (fig. 284) is a strong dense band, 

 composed of fine fibres massed together into a membranous structure. It 

 extends from the upper (medial) border of the first costal cartilage (and rib), 



Fig. 284. — Posterior View of the Sterno-costo-clavicular Joint. 



Costo- 

 clavicular 

 Posterior ligament 

 portion of 

 Interclavicular capsule 

 ligament J^s- 



upward, backward, and distinctly laterally to the costal tuberosity on the under 

 surface of the medial extremity of the clavicle, to which it is attached just lateral 

 to the lower part of the capsule. Frequently some of the lateral fibres pass up- 

 ward and medially behind the rest, and give the appearance of decussating. It 

 is from half to three-quarters of an inch (1.5-2 cm.) broad. 



The articular disc (fig. 285) is a flattened disc of nearly the same size and 

 outline as the medial articular end of the clavicle, which it fairly accurately 

 fits. It is attached above to the upper border of the posterior edge of the clavicle; 

 and below to the cartilage of the first rib at its union with the sternum, where it 

 assists in forming the socket for the clavicle. At its circumference it is connected 

 with the articular capsule, and this connection is very strong behind, and still 

 stronger above, where it is blended with the interclavicular ligament. 



It is usually thinnest below, where it is connected with the costal cartilajre. It varies in 

 thickness in different parts, sometimes being thinner in the centre than at the circumference 

 sometimes the reverse, and is occasionally perforated in the centre. It divides the joint into 

 two compartments. 



There are two synovial membranes (fig. 285) ; a lateral one, which is reflected 

 from the clavicle and capsule over the lateral aspect of the disc and is looser 

 than the medial one; the medial is reflected from the sternum over the medial 

 side of the articular disc, costal cartilage, and capsule. Occasionally a communi- 

 cation takes place between them. 



The arterial supply is derived from branches — (1) from the internal mammary; (2) from 

 the superior thoracic branch of the axillary; (3) twigs of a muscular branch often arising from 

 the subclavian artery pass over the interclavicular notch; (4) twigs of the transverse scapular 

 (suprascapular) artery. 



The nerve-supply is derived from the nerve to the subclavius and sternal descending branch 

 of the cervical plexus. 



