Part 5 (2/2)

It is flat, thin, and of a triangular form. This bone lies upon and is retained in its position by muscles. By their contractions it may be moved in different directions.

99. The HUMERUS is cylindrical, and is joined at the elbow with the ulna of the fore-arm; at the scapular extremity, it is lodged in the _glenoid_ cavity, where it is surrounded by a membranous bag, called the _capsular ligament_.

95-104. _Give the anatomy of the bones of the upper extremities._ 95.

Give the structure of the bones of the extremities. 96. How many bones in the upper extremities? Name them. 97. Give the attachments of the clavicle. What is its use? 98. Describe the scapula. How is it retained in its position? 99. Describe the humerus.

[Ill.u.s.tration: Fig. 13. 1, The shaft of the humerus. 2, The large, round head that is placed in the glenoid cavity. 3, 4, Processes, to which muscles are attached. 5, A process, called the external elbow. 6, A process, called the internal elbow. 7, The articulating surface upon which the ulna rolls.]

[Ill.u.s.tration: Fig. 14. 1, The body of the ulna. 2, The shaft of the radius. 3, The upper articulation of the radius and ulna. 4, Articulating cavity, in which the lower extremity of the humerus is placed. 5, Upper extremity of the ulna, called the olecranon process, which forms the point of the elbow. 6, s.p.a.ce between the radius and ulna, filled by the intervening ligament. 7, Styloid process of the ulna. 8, Surface of the radius and the ulna, where they articulate with the bones of the wrist.

9, Styloid process of the radius.]

100. The ULNA articulates with the humerus at the elbow, and forms a perfect hinge-joint. This bone is situated on the inner side of the fore-arm.

What is represented by fig. 13? By fig. 14? 100. Describe the ulna.

101. The RADIUS articulates with the bones of the carpus and forms the wrist-joint. This bone is situated on the outside of the fore-arm, (the side on which the thumb is placed.) The ulna and radius, at their extremities, articulate with each other, by which union the hand is made to rotate, permitting its complicated and varied movements.

102. The CARPUS is composed of eight bones, ranged in two rows, and so firmly bound together, as to permit only a small amount of movement.

[Ill.u.s.tration: Fig. 15. U, The ulna. R, The radius. S, The scaphoid bone.

L, The semilunar bone. C, The cuneiform bone. P, The pisiform bone. These four form the first row of carpal bones. T, T, The trapezium and trapezoid bones. M, The os magnum. U, The unciform bone. These four form the second row of carpal bones. 1, 1, 1, 1, 1, The metacarpal bones of the thumb and fingers.]

[Ill.u.s.tration: Fig. 16. 10, 10, 10, The metacarpal bones of the hand. 11, 11, First range of finger-bones. 12, 12, Second range of finger-bones.

13, 13, Third range of finger-bones. 14, 15, Bones of the thumb.]

103. The METACARPUS is composed of five bones, upon four of which the first range of the finger-bones is placed; and upon the other, the first bone of the thumb. The five metacarpal bones articulate with the second range of carpal bones.

101. The radius. 102. How many bones in the carpus? How are they ranged? 103. Describe the metacarpus.

104. The PHALANGES of the fingers have three ranges of bones, while the thumb has but two.

_Observation._ The wonderful adaptation of the hand to all the mechanical offices of life, is one cause of man's superiority over the rest of creation. This arises from the size and strength of the thumbs, and the different lengths of the fingers.

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