in TIN-: M;TI<TI..\TI- 



thoro is tho atmospheric pressure, whose influence is (if a certain impor- 

 tuner. This nuiy bo proved by removing all tho surrounding muscles, uln n 

 it will be found that the capsule is not relaxed, nor are tho articular suifurrs 

 separated; to effect this, it is necessary to make an owning in the r;ijnli-, 

 so as to allow the air to outer its cavity, when the surfaces immediately 

 separate. 



Synovia! capsule. This is very loose, and entirely enveloped by tho 

 peripheral capsule, whose internal surface it lines. 



Movements. Like all the enarthrodial articulations, tho scapulo -humeral 

 permits extension, flexion, abduction, adduction, circumduction, and i-t<iti<>n. 

 These various movements, however, are far from being so extensive us in 

 Man, the arm in the domesticated animals not being <1< turln ! i'mm tin: 

 trunk, but being, on tho contrary, fixed with the shoulder against tho lut< nil 

 parietos of the thorax. Flexion and extension are the least limited and tin: 

 most frequently repeated movements; their execution always demunds a 

 displacement of tho two bones, which are almost equally movable. In Jl> 

 the scapulo-humcral angle is closed, not only because the inferior extremity 

 of the humerus is carried backwards and upwards, but also because tho 

 scapula pivots on its superior attachments in such a manner as to throw its 

 glenoid angle forward and upward. Extension is produced by an inverse 

 mechanism. During tho execution of the other movements, tho scapula 

 remains fixed, and the humerus alone is displaced, bringing with it the 

 inferior rays of the limbs. If it is carried outwards, we have abduction, 

 or inwards, adduction; if the member passes successively from flexion to 

 abduction, and from that to extension, etc., in describing a circle by its 

 lower extremity, then there is circumduction ; if it pivots from left to right, 

 or right to left, we have rotation. 



In the Fig, Dog, and Cat, the synovial membrane is not exactly inclosed by tho 

 fibrous capsule, but forms in front a cul-de-sac, which descends iu the bic'pital groove to 

 favour the gliding of the coraco-radial tendon. 



In Mnn. the scapulo-humeral articulation is disposed as in animals, but it is :il><> 

 protected above by the coraco-acromion roof. For the reasons noted alxivc, thin 

 articulat : on allows of moro extensive motion than in animals. As remarked l>y 

 Cruveilhier, of all the joints in the human body, the scapulo-liumcral is that which 1ms 

 the most extensive motion ; in movements forward and outward, the humerus can 

 become horizontal ; in those of circumduction it describes a complete cone, which iu 

 more extensive in front and laterally than behind and inwardly. 



2. Humero-radial, or Elbow Articulation. 



(Preparation. Turn down the inferior extremity of the flexors of the fore-arm, 

 remove the olecranian, epicondyloid, and epitrochlcan muscles, taking care not to 

 damage the ligaments to which they somewhat clos ly adhere.) 



Three bones concur to form this articulation, which presents a remark- 

 able example of an angular ginglymus : the humorus, by its inferior ex- 

 tremity, and the two bones of tho arm by their upper extremities. 



Articular surfaces. Tho humeral surface, already described at page 74, 

 is transversely elongated, and convex from before to behind. It presents : 

 1, A median groove excavated by a synovial fossette; 2, An external groove 

 (humeral trochlca) not so deep as tho preceding; 3, A kind of voluminous 

 condyle which borders, inwardly, tho internal pulley, and whoso untrru 

 posterior diameter is much greater than that of the external lip of tho 

 trochlea of the opposite side. Tho anlibrachial surface, divided into two 

 portions, is moulded to the humeral surface ; it is, therefore, concave before 

 and Ix-lii ml, and is composed : 1, Of a double external groove ; 2, Of an 



