134 ARTICULATIONS OF THE UPPER LIMB. 



of it. The movements which take place in the superior and inferior compartments 

 of the joint are of different kinds. In the upper the fibro-cartilage glides backwards 

 and forwards on the temporal bone ; in the lower compartment the condyle rotates 

 on a transverse axis against the fibro-cartilage. In opening the mouth the two move- 

 ments are combined : the jaw and fibro-cartilage together move forwards and rest on 

 the convex root of the zygoma, while at the same time the condyle revolves on the 

 fibro-cartilage. When the lower incisors are protruded beyond those of the upper 

 jaw, the movement is confined chiefly to the upper articulation; and when the same 

 movement is alternately performed in the joints of opposite sides a horizontal or 

 grinding motion is produced. The fibres of the external lateral ligament remain 

 tight both in shutting and opening the mouth, and it is owing to their direction that 

 in opening the mouth the condyle is driven forwards. 



ARTICULATIONS OF THE UPPER LIMB. 



THE SCAPULO-CLAVICULAR ARCH. 



The supporting arch of the upper limb has only one point of attachment 

 to the trunk, namely, that at the steruo-clavicular articulation ; the scapula 

 being connected with the trunk only by muscles. 



The clavicle articulates at its inner end with the first bone of the 

 sternum, and is connected by ligaments to its fellow of the opposite side 

 and to the first rib. At its outer end it is united to the scapula. 



STERNO-CLAVICULAR ARTICULATION". The articular surface of the inner 

 end of the clavicle is considerably larger than the opposing surface of the 

 sternum. Between the two bones an interarticular fibro-cartilage is interposed. 



The anterior sterno-clavicular ligament, broad and consisting of parallel 

 fibres, passes from the inner extremity of the clavicle in front downwards 

 and inwards, upon the anterior surface of the sternum. 



The posterior sterno-clavicular ligament, lying on the thoracic aspect of the 

 joint, is of similar conformation with the anterior ligament, but is not so 

 broad or strongly marked. 



The interarticular fibro-cartilage, nearly circular in its form, and thicker 

 above and at the border than at the centre, is interposed between the arti- 

 culating surfaces of the sternum and clavicle. Towards its upper part it is 

 attached to the inner and upper part of the clavicle, and at its lower edge 

 to the cartilage of the first rib. In the latter situation it is thin and some- 

 what prolonged, so that the inferior border of the clavicle rests upon it. 



Synovial membranes. In this articulation, as in that of the lower jaw, 

 there are two cavities lined by synovial membrane, one on each side of the 

 interarticular fibro-cartilage. 



The interclavicular ligament is a dense fasciculus of fibres, between the 

 contiguous extremities of the clavicles. It dips downwards in the middle, 

 and is connected with the upper margin of the sternum, filling up a part of 

 its interclavicular notch. 



The costo-clavicular ligament (ligamentum rhomboides Weitbrecht) does 

 not properly form part of the sterno-clavicular articulation ; yet it con- 

 tributes materially to retain the clavicle in its situation. It is attached 

 iuferiorly to the cartilage of the first rib near its sternal end, and passes 

 obliquely backwards and upwards, to be fixed to a rough depression at the 

 under surface of the clavicle near the sternal end. 



SCAPULO-CLAVICULAR CONNECTIONS. At its outer end the clavicle articu- 

 lates with the acromion, and is connected by ligamentous fibres with the 

 coracoid process. 



The acromio- clavicular articulation is a synovial joint uniting the outer 



