208 ARTICULATIONS. 



tion of the Sterno-cleido-mastoid and the integument; behind, it is in relation 

 with the interarticular fibro-cartilage and the two synovial membranes. 



The Posterior Sterno-clavicular Ligament is a broad band of fibres, which covers 

 the posterior surface of the articulation, being attached, above, to the posterior 

 part of the inner extremity of the clavicle ; and, passing obliquely downwards 

 and inwards, is connected, below, to the posterior and upper part of the sternum. 

 It is in relation, in front, with the interarticular fibro-cartilage and synovial mem- 

 branes ; behind, with the Sterno-hyoid and Sterno-thyroid muscles. 



The Interclavicular Ligament is a flattened ligamentous band, which varies 

 considerably in form and size in different individuals ; it passes from the upper 

 part of the inner extremity of one clavicle to the other, and is closely attached to 

 the upper margin of the sternum. It is in relation, in front, with the integument; 

 behind with the Sterno-thyroid muscles. 



The Costo-clavicular or rhomboid Ligament is a short, flat, and strong band of 

 ligamentous fibres of a rhomboid form, attached, below, to the upper and inner 

 part of the cartilage of the first rib ; and, ascending obliquely backwards and out- 

 wards, is attached, above, to the rhomboid depression on the under surface of the 

 clavicle. It is in relation, in front, with the tendon of origin of the Subclavius ; 

 behind, with the subclavian vein. 



The Interarticular Fibro-cartilage is a flat and nearly circular disk, interposed 

 between the articulating surfaces of the sternum and clavicle. It is attached, 

 above, to the upper and posterior border of the clavicle ; below, to the cartilage 

 of the first rib, at its junction with the sternum ; and by its circumference to the 

 anterior and posterior sterno-clavicular ligaments. It is thicker at the circum- 

 ference, especially its upper and back part, than at its centre, or below. It 

 divides the joint into two cavities, each of which is furnished with a separate 

 synovial membrane ; when the fibro-cartilage is perforated, which not unfrequently 

 occurs, the synovial membranes communicate. 



Of the two Synovial Membranes found in this articulation, one is reflected from 

 the sternal end of the clavicle, over the adjacent surface of the fibro-cartilage, and 

 cartilage of the first rib ; the other is placed between the articular surface of the 

 sternum and adjacent surface of the fibro-cartilage. The latter is the more loose 

 of the two ; they seldom contain much synovia. 



Actions. This articulation is the centre of the movements of the shoulder, and 

 admits of motion in nearly every direction, upwards, downwards, backwards, 

 forwards, as well as circumduction ; the sternal end of the clavicle and the inter- 

 articular cartilage gliding on the articular surface of the sternum. 



2. SCAPULO-CLAVICULAR AETICULATION. 



The Scapulo-clavicular is an arthrodial joint, formed between the outer ex- 

 tremity of the clavicle, and the upper edge of the acromion process of the scapula. 

 Its ligaments are the 



Superior Acromio-clavicular. 

 Inferior Acromio-clavicular. 



Coraco-clavicular \ ^ P.? 

 ( Conoid. 



Interarticular Fibro-cartilage. 



The Superior Acromio-clavicular Ligament is a broad band of fibres, of a quad- 

 rilateral form, which covers the superior part of the articulation, extending 

 between the upper part of the outer end of the clavicle, and the adjoining part of 

 the acromion. It is composed of parallel fibres, which interlace with the 

 aponeurosis of the Trapezius and Deltoid muscles ; below, it is in contact with 

 the interarticular fibro-cartilage and synovial membranes. 



The Inferior Acromio-clavicular Ligament, somewhat thinner than the preceding, 

 covers the under part of the articulation, and is attached to the adjoining surfaces 



