ARTICULATIONS OF THE ANTERIOR LIMBS. 155 



ments in such a manner as to throw its glenoid angle forward and upward. 

 Extmsion is produced by an inverse mechanism. During the execution of the 

 other movements, the scapula remains fixed, and the humerus alone is displaced, 

 bringing with it the inferior bones of the limb. If it is carried outwards, we 

 have abdicction, or inwards, addurtmi ; if the leg passes successively from flexion 

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

 exti-emity, then there is circumduction ; if it pivots from left to right, or right to 

 left, we have rotation. 



In the Pig, Dog, and Cat, tlie synovial membrane is not exactly enclosed by the fibrous 

 capsule, but forms in front a cul-de-sac, which deaceuda in the bicipital gi-oove to favour the 

 gliding of the coraco-radialia tendon. 



In Man, the scapulo-liumenil articulation ia disposed as in animals, but it is also protected 

 above by the coraco-acromion arch. For the reaaoiia noted above, this articulation allows of 

 more extensive motion thun in animals. As remarked by Cruveilhier, of all the joints in the 

 human body, the scapulo-humeral is that which has the most extensive motion; in movements 

 forward and outward, the humerus can become horizontal ; in those of circumductioa it 

 describes a complete cone, which is more extensive in front and laterally than behind and 

 inwardly. 



2. HUMERO-RADIAL, OR ElBOW ARTICULATION (Fig. 128). 



{Preparation. — Turn down the inferior extremity of the flexors of the forearm, remove the 

 olecranian, epicondyloid, and epitrochlean muscles, taking care not to damage the ligaments 

 to which they somewhat closely adhere.) 



Three bones concur to form this articulation, which presents a remarkable 

 example of an angular ginglymus : the humerus, by its inferior extremity, and 

 the two bones of the arm by their upper extremities. 



Articular surfaces. — The humeral surface^ already described at page 102, 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 

 trochlea) not so deep as the preceding. 8. A kind of voluminous condyle which 

 borders, inwardly, the internal pulley, and whose antero-posterior diameter is 

 much greater than that of the external lip of the trochlea of the opposite side. 

 The antibrachial surface, divided into two portions, is moulded to the humeral 

 surface ; it is, therefore, concave before and behind, and is composed : 1. Of a 

 double external groove. 2. Of an internal glenoid cavity, both excavated, on the 

 superior extremity of the radius. 3. A middle ridge for the middle groove of 

 the humerus, separating the two preceding surfaces, and prolonged on the ulnar 

 beak, where it forms the sigmoid notch. Tliis ridge shows a small synovial 

 fossette hollowed out on the radius and ulna. 



^fode of union. — Three ligaments : two lateral and an anterior. 



a. The external lateral ligament (Figs. 128, 8) is a thick, short, and strong 

 funicle, attached above to the crest limiting outwardly and posteriorly the musculo- 

 spiral groove, and in the small cavity placed at the external side of the humeral 

 articular surface. Below, it is inserted into the supero-external tuberosity of the 

 radius. Its anterior border is confounded with the capsular ligament, and is 

 margined by the principal extensor of the phalanges, which derives from it 

 numerous points of attachment. By its posterior border it is in contact with 

 the external flexor of the metacarpus. Its internal face is lined by synovial 

 membrane, and its external face is only separated from the skin by the anti- 

 brachial aponeurosis, and some of the fasciculi from the origin of the lateral 

 extensor muscle of the phalanges. Its superficial fibres are vertical, and are 



