THE ELBOW-JOIXT 227 



within the capsule, surrounded only by a tubular process of synovial membrane. 

 It is fiat, ■with the surfaces looking upwards and downwards, until it reaches the 

 bicipital groove, when it assumes a rounded form. It strengthens the articulation 

 along the same course as the coraco-hvuneral ligament, and tends to prevent the head 

 of the humerus from being pulled upwards too forcibly against the under 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 Ijone, from which it cannot escaj)e on account 

 of the abutting tuberosities and the strong transverse humeral ligament Avhich 

 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 glenoid socket; and, more- 

 over, 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 pull the head of 

 the humerus below the lower edge of the cavity. 



4. THE ELBOW-.JOINT 

 Class, — Diarthrosis. Subdivision. — Ginglymus. 



The elbow is a complete hinge, and, unlike the knee, depends for its security 

 and strength upon the configuration of its bones rather than on the numljer, 

 strength, or arrangement of its ligaments. The bones composing it are the lower 

 end of the humervis al:)Ove, and the upper ends of the radius and ulna below; the 

 articular surface of the humerus being received partly within the great sigmoid 

 ca\dty of the ulna, and partly upon the cup-shaped surface of the radius. The 

 ligaments form one large and capacious capsule, which, by blending with the 

 orlncular 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 consideral;)ly strengthened by superadded fibres arising from the 

 condyles of the humerus and inseparal)ly connected with the capsule. For con- 

 venience of description it will be sjioken of as consisting of four portions: — 



Anterior. Internal. 



Posterior. External. 



The anterior portion (fig. 228) 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 ridges which start from the front of the internal and external 

 condyles, and meet at a variable distance aljove the coronoid fossa. Below, it is 

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

 intimately blended Avith the front of the orbicular ligament, a few fibres passing 

 on to the neck of the radius. It varies in strength and thickness, being sf>me- 

 times so thin as l:)arely to cover the synovial membrane; at others, thick and strong, 

 and formed of coarse decussating filjres, the majority of which descend from the 

 inner side outwards to the radius. 



The posterior portion (fig. 229), thin and membranous, is attached superiorly 

 to the humerus, in much the same inverted V-shaped way as the anterior; ascend- 

 ing from the internal condyle, along the inner side of the olecranon fossa nearly 

 to the top; then, crossing the bottom of the fossa, it descends on the outer side, 

 skirting the outer margin of the trochlear surface, and turns outwards along the 

 ]MjSterior edge of the capitellum. Inferiorly, it is attached to a slight groove along 

 the superior and external surfaces of the olecranon, and the rough surface t)f the 

 ulna just beyond the lesser sigmoid notch, and Avith the orlncular ligament, a few 

 fibres ])assing on to the neck of the radius. It is composed of decussating fibres, 

 most of which pass vertically or obliquely downwards, a few taking a transverse 

 course at the summit of the olecranon fossa where the ligament is usually thinnest. 



The internal portion (fig. 228) is thicker, stronger, and denser than either the 

 anterior or posterior ])ortions. It is triangular in form, its apex being attached to 

 the anterior and under aspect of the internal condyle, and to the condyloid edge of 



