258 THE ARTICULATIONS 



is raised to a right angle with the trunk, and extension shortly after the humerus passes the line 

 of the trunk. 



Further elevation of the arm beyond the right angle, in the abducted or extended position, 

 is effected by the rotation of the scapula round its own axis by the action of the trapezius and 

 serratus anterior muscles upon the sterno-clavicular and acromio-clavicular joints respectively. 



The acromion and coracoid process, together with the coraco-acromial ligament, form an 

 arch, which is separated by a bursa and the tendon of the supraspinatus from the capsule of 

 the shoulder. Beneath this arch the movements of the joint take place, and against it the head 

 and tuberosities are pressed when the weight of the trunk is supported by the arms; the greater 

 tuberosity and the upper part of the shaft impinge upon it when abduction and extension are 

 carried to their fullest extent. 



Xo description of the shoulder-joint would be complete without a short notice of the peculiar 

 relation which the biceps tendon bears to the joint. It passes over the head of the humerus a 

 little to the medial side of its summit, and hes free within the capsule, surrounded only by a 

 tubular process of synovial membrane. It is flat, with the surfaces looking upward and down- 

 ward, until it reaches the intertubercular (bicipital) groove, when it assumes a rounded form. 

 It strengthens the articulation along the same course as the coraco-humeral Ugament, and tends 

 to prevent the head of the humerus from being pulled upward too' forcibly against the inferior 

 surface of the acromion. It also serves the purpose of a ligament by steadying the head of the 

 humerus in various movements of the arm and forearm, and to this end is let into a groove at 

 the upper end of the bone, from which it cannot escape on account of the abutting tuberosities 

 and the strong transverse humeral ligament which binds it down. Further, it acts like the four 

 shoulder muscles which pass over the capsule, to keep the head of the humerus against the glen- 

 oid socket; and, moreover, it resists the tendency of the pedoralis major and latissimus dorsi 

 muscles, in certain actions when the arm is away from the side of^the body, to puU the head of 

 the humerus below the lower edge of the cavity. 



Muscles which act upon the shoulder-joint. — Flexors or protractors. — Deltoid (anterior 

 fibres), pectoralis major (clavicular fibres), coraco-brachiaUs, biceps (short head),subscapularis 

 (upper fibres). 



Extensors or retractors. — ^Latissimus dorsi, deltoid (posterior fibres), teres major, teres minor, 

 infraspinatus (lower fibres). 



[Abductors. — Deltoid, supraspinatus, biceps (long head). 



Adductors. — Pectoralis major, latissimus dorsi, subscapularis, infraspinatus, teres major, 

 teres minor, coraco-brachialis, biceps (short head), triceps (lower head). 



Medial rototors.— Pectoralis major, latissimus dorsi, teres major, subscapularis, deltoid 

 (anterior fibres). 



Lateral rotators. — Deltoid (posterior fibres), infraspinatus, teres minor. 



Circumductors. — The above groups acting consecutively. 



4. THE ELBOW-JOINT 

 Class. — Diarthrosis. Subdivision. — Ginglymus. 



The elbow [articulatio cubiti] is a complete hinge, and, unlike the knee, 

 depends for its security and strength upon the configuration of its bones rather 

 than on the number, strength, or arrangement of its ligaments. The bones 

 composing it are the lower end of the humerus above, and the upper ends of the 

 radius and ulna below; the articular surface of the humerus being received 

 partly within the semilunar notch (great sigmoid cavity) of the ulna, and partly 

 upon the cup-shaped area (fovea) of the radial head. The ligaments form one 

 large and capacious capsule [capsula articularis], which, by blending with the 

 annular ligament, and then passing on to be attached to the neck of the radius, 

 embraces the elbow and the superior radio-ulnar joints, uniting them into one. 

 Laterally, it is considerably strengthened by superadded fibres arising from the 

 epicondyles of the humerus and inseparably connected with the capsule. For 

 convenience of description it will be spoken of as consisting of four portions: — 



Anterior. Medial. 



Posterior. Lateral. 



The anterior portion (fig. 293) is attached to the front of the humerus above 

 the articular surface and coronoid fossa, in an inverted V-shaped manner, to two 

 very faintly marked ridgos which start from the front of the medial and lateral 

 epicondyles, and meet a variable distance above the coronoid fossa. Below, it is 

 fixed, just beyond the articular margin, to the front of the coronoid process and it 

 is intimately blended with the front of the annular ligament, a few fibres passing 

 on to the neck of the radius. 



It varies in strength and thickness, being sometimes so thin as barely to cover the synovial 

 membrane; at others, thick and strong, and formed of coarse decussating fibres, the majority 

 of which descend from the medial side laterally to the radiug. 



