View of the ligaments connecting the ulna and radius at
their upper part. 1. The radius; 2. the ulna; 3. the coronary
ligament surrounding the head of the radius; 4. the
oblique ligament passing from the ulna to the tubercle of
the radius; 5 the upper portion of the interosseous ligament.
161. At their inferior extremities the ulna and radius are united partly by the interosseous ligament (fig. LXXVII. 1) and partly by ligamentous fibres which pass transversely from one bone to the other (fig. LXXVII. 2) on the anterior and the posterior surface of the fore-arm.
1. Interosseous ligament; 2. transverse fibres passing
between the radius and ulna, and uniting the two bones;
3. 4. 5. posterior and lateral ligaments of the wrist joint;
6. ligaments uniting the bones of the wrist with one another;
7. 8. ligaments which attach the metacarpal to the
carpal bones; 9. transverse ligaments for the attachment
of the phalanges of the fingers; 10. lateral ligaments for
the attachment of the phalanges of the fingers 11. ligaments
of the thumb.
162. The lower extremity of the radius is also united to the wrist; and the hand being attached to the wrist, the junction of the hand and the fore-arm is effected by the articulation of the wrist with the radius (fig. LXXVII.). The ligaments which connect the bones of the wrist with the radius are bands of exceeding strength (fig. LXXVII. 3).
163. The muscles that act upon the fore-arm are placed upon the arm (fig. LXXVIII.). The joint of the elbow being a hinge-joint, the fore-arm can admit only of two motions, namely, flexion and extension. The muscles by which these motions are effected are four, two for each; the two flexors being placed on the fore part (fig. LXXVIII. 2. 4), and the two extensors on the back part of the arm (fig. LXXIX. 5).
164. The two flexor muscles of the fore-arm are termed the biceps and the brachialis (fig. LXXVIII. 2, 4). The biceps is so called because it has two distinct heads or points of origin (fig. LXXVIII. 2), both of which arise from the scapula (fig. LXXVIII. 2). About a third part down the humerus the two heads meet, unite and form a bulky muscle (fig. LXXVIII. 2), which, when it contracts, may be felt like a firm ball on the fore part of the arm, the upper part of the ball marking the point of union of the two heads (fig. LXXVIII. 2). The muscle gradually becoming smaller, at length terminates in a rounded tendon (fig. LXXVIII. 3), which is implanted into the tubercle of the radius a little below its neck (fig. LXXVIII. 3). It is an exceedingly thick and powerful muscle, and its manifest action is to bend the fore-arm with great strength. But since its tendon is inserted into the radius, besides bending the fore-arm, it assists other muscles that also act upon the radius in the performance of a function to be described immediately (168).
