218 



THE ARTICULATIONS 



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

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

 along the }»osterior asi)eet of the iip]ier 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 tlie i)assage of a small artery and vein. 



The rhomboid or costo-clavicular ligament (figs. 219 and 220) is a strong 

 dense band, composed of fine fibres massed together into a membranous structure. 

 It extends from the anterior edge of the upper border of the first costal cartilage, 

 upwards, backwards, and distinctly outwards to the rhomboid impression on the 

 \mder surface of the inner extremity of the clavicle, to which it is attached just 

 external to the lower part of the capsule. Freciuently some of the outer fibres i)ass 

 upwards and inwards behind the rest, and give the appearance of decussating. It 

 is from half to three-({uarters of an inch (1-5-2 cm.) broad. 



The interarticular fibro-cartilage (figs. 220 and 221) is a flattened disc of 

 nearly the same size and outline as the inner 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 



Fro. 221. — Section through Stekko-clavici'lar .Joint. 



The interarticular 

 flbro-eartilage 



The joint between 

 the sternum and 

 second costal car- 

 tilage 



Sternum, where it assists in forming the socket for the clavicle. At its circum- 

 ference it is connected with the capsular ligament, and this connection is very 

 strong behind, and still stronger above where it is blended Avith the interclavicular 

 ligament. It is usually thinnest below, where it is connected with the costal 

 cartilage. It varies in thickness in different parts, sometimes being thinner in the 

 centre than at the circumference, sometimes the reverse, and is occasionally per- 

 forated in the centre. It divides the joint into two compartments. 



There are two synovial membranes (figs. 220 and 221): an outer one, Avhich 

 is reflecti-d from the clavicle and cajisule over the outer side of the fibro-cartilage, 

 and is looser than the inner; the inner is reflected from the sternum over the inner 

 side of the fibro-cartilage, costal cartilage, and capsule. Occasionally a connnuni- 

 cation takes ](lai-e lictween tlieni. 



The arterial supply is derived from branches (l) from the internal niammarv; 

 (2) from the su]..'ri(.r thf)raeic branch of the axillary; (3) twigs of a muscul'ar 

 branch often arising from the subclavian artery pass over the interclavicular 

 notcli; (4) twigs of the suprascapular artery. 



The nerve-supply is derived from the nerve to the suhdavins and sternal 

 descending liranch of the cervical plexus. 



The movements permitted at this joint are various, though limited owing to 

 the capsular ligament being iiKjderately tense in every position of the clavicle. 



