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 14 On the Spine and its Various Bones

The reason for the large number of bones

Now why the spine is made not from two or three bones as long as the humerus in the arm with the ulna and the radius, or the femur in the leg with the tibia and fibula, but from thirty-four bones 17 differently articulated with each other, must be considered at this point with a view to the paramount component of the whole spine, now that our account is begun. This component is the dorsal medulla [medulla spinalis] (three figs. at the beginning of ch. 11, Bk. 4), which we shall endeavor to show, when we explain the series of nerves in Book Four, is like a brain for the parts located beneath the head. Because it was necessary that like the brain this be sheltered by a hard protective covering that would readily ward off injuries, the spine needed to be carved altogether like a keel placed beneath the human body, and at the same time a pathway, an extremely safe fortification, and as the Greeks say a su/rigc i(era/ 18 needed to be made for the medulla itself. Its nature resembles that of the brain, and the ills that beset a person when it is affected are comparable to those which we daily see occur when the brain is damaged. For the movements and sensation of all parts below the damaged vertebra are impaired. Galen attests that this is generally known. The divine Hippocrates instructs us in his book De articulis that if several contiguous vertebrae are displaced, it is serious, but if one moves out of alignment with the others, it is fatal; this is by no means well known to all. Hippocrates instructs us about the cause of a symptom: if several vertebrae are displaced at once, so that each moves slightly and is out of place, then there occurs a curved or not severe distortion of the dorsal medulla. If, though (he says), one of the vertebrae is displaced from its position, the dorsal medulla is diverted for a short distance and is damaged; the vertebra that moved will compress it if it does not also break it. 19 Since, therefore, the dorsal medulla cannot tolerate an angular bending that is sudden and sharp, the spine cannot be moved by means of large, loose joints having considerable movement without suffering damage. Therefore it was better for the spine to be built up of many small bones, each of which contributes to movement.



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 14 On the Spine and its Various Bones