286 ARTICULATIONS. 



above, to the rhomboid depression on the under surface of the clavicle. It ig 

 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 cir- 

 cumference, 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 fibre-cartilage is perforated, which not unfre- 

 quently 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, back- 

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

 the interarticular cartilage gliding on the articular surface of the sternum. 



II. SCAPULO-CLAVICULAR ARTICULATION. (Fio. 198.) 



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

 extremity of the clavicle, and the upper edge of the acromion process of the 

 scapula. Its ligaments are the 



Superior Acromio-clavicular. 

 Inferior Acromio-clavicular. 



{Trapezoid 

 and 

 Conoid. 

 Interarticular Fibro-cartilage. 



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

 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 acro- 

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

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

 articular fibro-cartilage and synovial membranes. 



The Inferior Acrom.io- clavicular Ligament, somewhat thinner than the pre- 

 ceding, covers the under part of the articulation, and is attached to the adjoin- 

 ing surfaces of the two bones. It is in relation, above, with the interarticular 

 fibro-cartilage (when it exists) and the synovial membranes ; below, with the 

 tendon of the Supraspinatus. These two ligaments are continuous with each 

 other in front and behind, and form a complete capsule around the joint. 



The Coraco-clavicular Ligament serves to connect the clavicle with the cora- 

 coid process of the scapula. It consists of two fasciculi, called the trapezoid 

 and conoid ligaments. 



The trapezoid ligament, the anterior and external 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 line 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 a projecting angle. 



The conoid ligament, the posterior and internal fasciculus, is a dense band of 

 fibres, conical in form, the base being turned upwards, the summit downwards. 

 It is attached by its apex to a rough depression at the base of the coracoid pro- 



