146 ARTICULATIONS OF THE ITPER LIMB. 



inferior compartments of the joint are of different kinds. In the upper the 

 fibro-cai-tilage glides backwards and forAvards 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 movements 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. 

 A\Tien the lower incisors are protnided beyond those of the upper jaw, the move- 

 ment is confined chiefly to the ujiper articulation ; and when the same movement 

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

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

 tight in opening the njouth. owing to the descent of the condyle when it pa^^ses 

 forwards on the articular eminence. 



ARTICULATIONS OF THE UPPER LIMB. 



THE SCAPULO-CLAVICULAR ARCH. 



The supporting arch of the npper limb has only one point of attach- 

 ment to the skeleton of the trunk, namely, that at the sterno-clavicular 

 articulation ; the scapula being connected with the ti'unk 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. 



Steiino-Clavicular Articulatiox. — The articular surface of the 

 inner end of the clavicle is considerably larger than the opposing sur- 

 face of the sternum. Between the two bones an interarticular fibro- 

 cartilage is interposed. 



Tlie 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, on the ]30sterior 

 aspect of the joint, is of similar conformation to the anterior ligament, 

 but is not so broad or strongly marked. 



The interclavicular ligament is a dense fasciculus of fibres passing 

 over the sternal ends of both clavicles. It dips downwards in the 

 middle, where it is attached to the interclavicular notch of the sternum. 



The interarticular jBlbro-cartilage, nearly circular in its form, and 

 thicker above and at its margins than at the centre, is interposed be- 

 tween the articulating surfaces of the sternum and clavicle. Towards 

 its upper part it is attached to the inner and U])per part of tlie clavicle, 

 and at its lower edge to the cartilage of the first rib. In the latter 

 sitnntion it is thin and prolonged out\Yards, beneath the inferior border 

 of the clavicle. 



Synovial mem'branes. — 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 costo-clavicular or rhomboid ligament does not properly 

 form part of the sterno-clavicular articulation ; yet it contributes ma- 

 terially to retain the clavicle in its situation. It is attached inferiorly 

 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 Articulations. — At its outer end the clavicle 

 ai'ticulates with the acromion and coracoid processes of the scapula. 



