Book One -- The things that sustain and support the entire body, and what braces and attaches them all. [the bones and the ligaments that interconnect them] | Chapter 22 On the Clavicles

Why the shoulder joint is kept away from the ribs; the use of the clavicle and acromion 21

For if the clavicle ran only posteriorly from the midpoint of its length [corpus claviculae], going out to the sides of the neck, and did not articulate with the upper tip [facies articularis acromii] of the scapular process, surely nothing would prevent the whole scapula, being unsecured by the clavicle, from falling over the thorax and being pressed against the side of the thorax, and the shoulder joint becoming extremely close to the ribs (you may find these in the skeletons where the joint of R with S is removed from the ribs by the joint of Q and l), and thereby a great many motions of the arm would be inhibited. For the arm is able to be moved in such a variety of different motions in man, in monkeys, and all the animals that have clavicles, because its joint with the scapula


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stands at a considerable distance from the side of the thorax. For if that joint touched the ribs of the chest, or were somehow placed next to them (as in quadrupeds), we would be unable to the circular movements of the arms and gesticulation to the chest, back, neck, and hips — which we know occurs when a dislocated humerus collapses onto the ribs or when a scapula hangs like a wing because of a fractured clavicle. 22 Lest, therefore, we be deprived of such necessary functions, Nature wished the joint of the humerus to be a good distance from the thorax, accomplishing this by the upper process of the scapula, which is so extended that when pushed from the thorax by the clavicle it is supported and stabilized, and the joint itself is by this means kept far away from the thorax.



Book One -- The things that sustain and support the entire body, and what braces and attaches them all. [the bones and the ligaments that interconnect them] | Chapter 22 On the Clavicles