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 16 On the Vertebrae of the Thorax

Why it was fitting that one vertebra be received on both sides in the middle of the spine

But at the same time it does not make much difference whether the twelfth or the eleventh or some other is received on both sides, so long as we do not overlook the signal craft of Nature, which fashioned a vertebra in the midst of the back, stable and supported on both ends just as we see builders place one stone between two others in vaulted and arched buildings which is supported on each side though it supports no stone itself, while all the others support one stone and are received and supported by another. 59 So that the spine might be moved in the ways assigned it, it is necessary that this vertebra supported on both sides be supported without moving while all the others retire slightly from it and from each other; for as it is unmoved when we flex the back, we draw the upper vertebrae downward and bend the lower ones somewhat upward. 60 In extension, we move the vertebrae back with an opposite motion, since the motions of the back 61 are carried out with a curving but not quite angular figure. You will readily see how little this agrees with the views of Galen in the thirteenth book of De usu partium if you compare the passages. 62 We shall explain the motions of the back together with its muscles, until now poorly understood, in the second book. 63 But now if we go back to the thoracic vertebrae, between the ascending and descending process on either side 64 rough places are plainly to be observed (around G in figs. 2, 3, 4) and irregularly protruding small processes, prepared so that strong ligaments 65 may start from here, more robustly and firmly binding the thoracic vertebrae together the more obscurely it was useful for the thoracic vertebrae to be moved than the cervical.



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 16 On the Vertebrae of the Thorax