BONES OF THE UPPER EXTREMITIES.
The shoulder-blade (scapula), the collar-bone (clavicle), the bone of the upper arm (humerus), the two bones of the forearm (ulna and radius), the bones of the wrist (carp bones), the bones of the palms of the hand (metacarpal bones), the bones of the thumb and fingers (phalanges), -- these are the bones of the upper limbs.
The collar-bone is fastened at one end to the breastbone, at the other end to the shoulderblade. It keeps the shoulders from dropping forward. Many persons allow it to fail of this end by getting very much bent in early life. This happens at school, when children are allowed to sit in a stooping posture. In the French, a race remarkable for a straight, upright figure, this bone is said to be longer than in any other people.
The shoulder-blade lies upon the upper part of the back, forming the shoulder. It has a shallow cavity (glenoid cavity), into which is inserted the head of the upper armbone. Several strong muscles are attached to the elevtions of this bone, which keep it in its place, and move it about as circumstances require.
The upper armbone has its round head fastened in the glenoid cavity, by the strong capsular ligament, forming a joint capable of a great number of movements. At the elbow it is united with the ulna of the forearm. It is a long, cylindrical bone, represented by Fig. 9: 1, is the shaft of the bone; 2, the large, round head which fits into the glenoicl cavity; 3 , the surface which unites with the ulna.
Of the two bones of the fore-arm, the ulna is on the inner side, and unites with the, humerus, making an excellent hingejoint. The other bone of the forearm, the radius, lies on the outside of the arm, -- on the same side with the thumb, -- and unites, or articulates, as we say, with the bones of the wrist. In Fig. 10: 1, is the body of the ulna; 2, the shaft of the radius; 4, the articulating surface, with which the lower end of the humerus unites; 5, the upper extremity of the ulna, called the olecranon process, which forms the elbow joint; 6, the point where the ulna articulates with the wrist.
The eight bones of the wrist or carpus are ranged in two rows, and being bound close together, do not admit of very free motion. InFig. 11: S is the scaphoid bone; L, the semilunar bone; C, the cuneiform bone; P, the pisiform bone; T, T, the trapezium and trapezoid bones; M, the os magnum; U, the ,uneiform bone. The last four form the second row of carpal bones. 11, 11, are the metacarpal bones of the hand; 2, 2, the first range of the fingerbones; 3, 3, the second range of fingerbones; 4, 4, the third range of finger bones; 5, 6, the bones of the thumb.
Of the five metacarpal bones, four are attached below to the first
range of the finger bones, and the other to the first bone of the thumb,
while the whole are united to the second range of the carpal bones
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