ELBOW-JOINT. 289 



the circumference of the cavity, the free edge being thin and sharp. It is con- 

 tinuous above with the long tendon of the Biceps muscle, which bifurcates at 

 the upper part of the cavity into two fasciculi, encircling the margin of the 

 glenoid cavity and uniting at its lower part. This ligament deepens the cavity 

 for articulation, and protects the edges of the bone. It is lined by the synovial 

 membrane. 



The Synovial Membrane lines the margin of the glenoid cavity and the fibro- 

 cartilaginous rim surrounding it ; it is then reflected over the internal surface 

 of the capsular ligament, covers the lower part and sides of the neck of the 

 humerus, and is continued a short distance over the cartilage covering the head 

 of the bone. The long tendon of the Biceps muscle which passes through the 

 joint, is inclosed in a tubular sheath of synovial membrane, which is reflected 

 upon it at the point where it perforates the capsule, and is continued around it 

 as far as the summit of the glenoid cavity. The tendon of the Biceps is thus 

 enabled to traverse the articulation, but is not contained in the interior of the 

 synovial cavity. The synovial membrane communicates with a large bursal 

 sac beneath the tendon of the Subscapularis, by an opening at the inner side 

 of the capsular ligament ; it also occasionally communicates with another bursal 

 sac, beneath the tendon of the Infraspinatus, through an orifice at its outer part. 

 A third bursal sac, which does not communicate with the joint, is placed be- 

 tween the under surface of the deltoid and the outer surface of the capsule. 



The Muscles in relation with the joint are, above, the Supraspinatus ; below, 

 the long head of the Triceps; internally, the Subscapularis; externally, the 

 Infraspinatus, and Teres minor ; within, the long tendon of the Biceps. The 

 Deltoid is placed most externally, and covers the articulation on its outer side,, 

 as well as in front and behind. 



The Arteries supplying the joint, are articular branches of the anterior and 

 posterior circumflex, and suprascapular. 



The Nerves are derived from the circumflex aud suprascapular. 



Actions. The shoulder-joint is capable of movement in every direction, for- 

 wards, backwards, abduction, adduction, circumduction, and rotation. 



Y. ELBOW-JOINT. 



The Elbow is a ginglymus or hinge-joint. The bones entering into its forma- 

 tion are the trochlear surface of the humerus, which is received in the greater 

 sigmoid cavity of the ulna, and admits of the movements peculiar to this joint, 

 those of flexion and extension, whilst the cup-shaped depression on the head of 

 the radius articulates with the radial tuberosity of the humerus, and the cir- 

 cumference of the head of the radius, with the lesser sigmoid cavity of the ulna, 

 allowing of the movement of rotation of the radius on the ulna, the chief action 

 of the superior radio-ulnar articulation. The articular surfaces are covered with, 

 a thin layer of cartilage, and connected together by the following ligaments : 



Anterior. Internal Lateral. 



Posterior. External Lateral. 



The Anterior Ligament (Fig. 199) is a broad and thin fibrous layer, which, 

 covers the anterior surface of the joint. It is attached to the fr.ont of the hu- 

 merus immediately above the coronoid fossa ; below, to the anterior surface of 

 the coronoid process of the ulna and orbicular ligament, being continuous on 

 each side with the lateral ligaments. Its superficial or oblique fibres pass from, 

 the inner condyle of the humerus outwards to the orbicular ligament. The 

 middle fibres, vertical in direction, pass from the upper part of the coronoid 

 depression, and become blended with the preceding. A third, or transverse 

 set, intersect these at right angles. This ligament is in relation, in front, with 

 the Brachialis Anticus ; behind, with the synovial membrane. 



The Posterior Ligament (Fig. 200) is a thin and loose membranous fold, at- 

 tached, above, to the lower end of the humerus, immediately above the olecra- 

 19 



