194 THE ARTICULATIONS. 



AeTICLE IV.---AETICULATIONS OF TRE ANTERIOR LiMBS. 



1. SCAPULO-HUMERAL ARTICULATION (Fig. 128). 



(Preparation. — Detach the limb from the trunk. Remove from the upper extremity those 

 muscles which are inserted in the vicinity of the glenoid cavity of the scapula ; turn down from 

 its lower extremity those which are inserted into the superior end of the humerus or a little 

 below, preserving the attachments of their tendons with the capsular ligament. The seapulo- 

 humeralis gracilis muscle may be allowed to remain, in order to show its relations.) 



To constitute this enarthrodial articulation, the scapula is united to the 

 humerus, and forms an obtuse angle which is open behind. 



Articular surfaces. — In the scapula there is the glenoid cavity — the shallow, 

 oval fossa, elongated in an antero-posterior direction, notched inwardly, and 

 excavated at its centre, or near the internal notch, by a small synovial f ossette. A 

 ligamentous band, attached to the brim of the cavity, fills up this notch, and is 

 the vestige of the glenoid ligament of Man. In the humerus, the articular head, 

 fixed between the large and small tuberosities, is often excavated by a shallow 

 synovial f ossette. 



Mode of union. — One capsular ligament (Fig. 128, 1), a kind of sac having two 

 openings — one inferior, embracing the head of the humerus ; and a superior, inserted 

 into the margin of the glenoid cavity. This capsule presents, in front, two sup- 

 porting fasciculi, which diverge as they descend from the coracoid process to the 

 great and small tuberosities. The aponeurotic expansion thus formed is very 

 thin and loose, so as to allow the two bones to separate to the extent of from 

 -f*Q to y^o of an inch ; but it is far from being sufficiently strong to bind them 

 firmly together. The articulation is, therefore, strengthened by the powerful 

 muscles which surround it, among which maybe noticed : 1. In front, the coraco- 

 radialis (flexor brachii), separated from the fibrous capsule by an adipose cushion. 

 2. Behind, the large extensor of the forearm and scapulo-humeralis gracilis (or 

 teres minor) muscles, the use of which appears to be to pull up this capsule during 

 the movements of flexion, so as to prevent its being pinched between the articular 

 surfaces. 3. Outwards, the short abductor of the arm and the infra-spinatus (postea 

 spinatus) tendon. 4. Inwards, the wide and strong tendon of the subscapularis 

 muscle. In addition to this powerful retaining apparatus, there is the atmospheric 

 pressure, the influence of which is of a certain importance. This may be proved 

 by removing all the surrounding muscles, when it will be found that the capsule 

 is not relaxed, nor are the articular surfaces separated ; to effect this, it is neces- 

 sary to make an opening in the capsule, so as to allow the air to enter its cavity, 

 when the surfaces immediately fall apart. 



Synovial capsule. — This is very loose, and entirely enveloped by the peripheral 

 capsule, the internal surface of which it lines. 



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

 permits extension, flexion, abduction, adduction, circumduction, and rotation. These 

 various movements, however, are far from being so extensive as in Man, the arm 

 in the domesticated animals not being detached from the trunk, but, on the 

 contrary, is fixed with the shoulder against the lateral parietes of the thorax. 

 Flexion and extension are the least limited, and the most frequently repeated 

 movements ; their execution always demands a displacement of the two bones, 

 wliich are almost equally movable. In flexion, the scapulo-humeral angle is 

 closed, not only because the inferior extremity of the humerus is carried back- 

 wards and upwards, but also because the scapula pivots on its superior attach- 



