Page:Encyclopædia Britannica, Ninth Edition, v. 1.djvu/893

Rh UPPER LIMB.] eapsular ligament lined by a synovial membrane, which is subdivided into anterior, posterior, internal, and ex ternal bands of fibres. Flexion and extension are the two movements of the joint, and the range of movement is limited by the locking at the end of flexion of the coronoid process into the coronoid fossa of the humerus, and at the end of extension of the olecranon process into the olecranoid fossa. The elbow joint is a hinge with screwed surfaces ; the path described by the hand and fore-arm is a spiral, so that during flexion they are thrown forwards and imvards. The muscles which cause the movements are inserted into the bones of the fore-arm. The flexors are the brachialis anticus, inserted into the coronoid of the ulna ; the biceps, which forms the fleshy mass on the front of the upper arm, into the tuberosity of the radius ; the supinator longus into the styloid process of the radius. The only extensor is the triceps-auconeus, which forms the fleshy mass on the back of the upper arm, and is inserted into the olecranon. oints ot The liadio-ulnar Joints are found between the two bones ire-arm. o f t ne fore-arm. The head of the radius rolls in the lesser sigmoid cavity of the ulna, and is retained in position by a ring-like ligament which surrounds it ; the shafts of the two bones are connected together by the interosseous membrane, their lower ends by a capsular ligament and a triangular fibro-cartilage or meniscus. The radius rotates round an axis drawn through the centre of its head and the styloid process of the ulna ; rotation of the fore-arm and hand forward is called pronation, rotation backwards, supination. The supinator and pronator muscles are all inserted into the radius : the supiuators are the longus and brevis and the biceps ; the pronators are the teres and quadratus. Where delicate manipulation is required the fore-arm is semi-flexed on the upper arm, for the cup- shaped head of the radius is then brought into contact with the capitellum of the humerus, and the rotatory movements of the bone can be performed with greater precision. /rist. The Wrist or Radio-carpal Joint is formed above by the lower end of the radius and the triangular meniscus, below by the upper articular surfaces of the scaphoid, semi-lunar, and cuneiform bones. An investing ligament, lined by a synovial membrane, and subdivided into anterior, posterior, internal, and external bands of fibres, encloses the joint. It is the oblong form of hinge-joint, and possesses two axes, a long and a short ; around the long axis movements occur which bend the hand forwards, or bring it in line with the fore-arm, or bend it backwards ; around the short axis the hand may be moved towards the radial or ulnar margins of the fore-arm. The flexors fonvard are the palmaris longus, inserted into the palmar fascia ; the flexor carpi radialis into the metacarpal bone of the index; the flexor carpi ulnaris into the pisiform bone; the extensors and flexors backwards are the longer and shorter radial extensors inserted into the metacarpal bones of the index and middle fingers, and the ulnar extensor into the meta carpal bone of the little finger ; the flexors and extensors of the fingers have also a secondary action on the wrist joint. The ulnar flexor and ulnar extensor of the wrist draw the hand to the ulnar side, and the radial flexor and extensor, together with the extensors of the thumb, draw the hand towards the radial border of the fore-arm, oints of The Carpal and Carpo-metacarpal Joints are constructed and - thus : The articular surfaces are retained in contact by certain ligaments passing between the dorsal surfaces of adjacent bones, by others between their palmar surfaces, and by interosseous ligaments between the semi-lunar and cuneiform, semi-lunar and scaphoid, os magnum and unci form, os magnum and trapezoid; lateral ligaments also attach the scaphoid to the trapezium, and the cuneiform to the unciform. Similarly, the trapezoid, os magnum, and 839 unciform are connected to the metacarpal bones of the fingers by dorsal, palmar, and interosseous ligaments, and the metacarpal bones of the fingers have a like mode of union at their carpal ends ; further, a transverse ligament extends between the distal ends of the metacarpal bones of the fingers, and checks too great lateral displacement. The range of movement at any one of these carpal joints is very slight, but the multiplicity of joints in this locality con tributes to the mobility of the wrist, and makes the junction, between the hand and fore-arm less rigid in its nature. The metacarpal bone of the thumb is not jointed to the index, and has a distinct saddle-shaped articulation with the trapezium, invested by a capsular ligament, so that its range of movement is extensive. The Metacarpo-phalangeal and Inter-plialangeal Joints Joints are connected by lateral ligaments passing between the fingers, bones, and by an arrangement of fibres on their dorsal and palmar surfaces. In studying the muscles which move the digits, it mil be advisable, on account of the freedom and importance of the movements of the thumb, to examine its muscles indepen dently. These muscles either pass from the fore-arm to the thumb, or are grouped together at the outer part of the palm, and form the elevation known as the ball of the thumb ; they are inserted either into the metacarpal bone or the pha langes. The thumb is extended and abducted, i.e., drawn away from the index, by three ex tensor muscles descending from the fore-arm, and inserted one into each of its three bones, and a small muscle, specially named abductor pollicis, in serted into the outer side of the first phalanx : its bones are bent on each other by a long and short flexor muscle ; it is drawn back to the index by an adductor muscle ; and the entire thumb is thrown FiQ.SsJ-DeepmusdeBof thepalmo* across the surface of the palm by the opponens pollicis, which is inserted into the shaft of the metacarpal bone. The four fingers can be either bent, or extended, or drawn asunder, i.e., abducted; or drawn together, i.e., adducted. The ungual phalanges can be bent by tho the hand. 1, abductor poliicis cut short; 2, opponens; 3 and 4, sub divisions of flexor brevis; 5, ad ductor ; 6, 6, tendon of long flexor pollicis ; 7, abductor of the little linger; 8, short flexor; 9, opponens; 10, tendon of flexor carpi ulnaris; 11, tendon of long supinator ; ft transverse metacarpal ligament. FIG. 24. Tendons attached to a finger, a, the extensor tendon; 6, deep flexor; c, superficial flexor; d, a lumbrical muscle;, an interosseous muscle; / tendinous expansion from the lumbrical and interosseous muscles joining the extensor tendon. action of the deep flexor muscle, the four tendons of which are inserted into them ; the second phalanges by the super ficial flexor, also inserted by four tendons, one into each phalanx ; these muscles descend from the front of the fore arm into the palm in front of the wrist, where they are