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 unequal size of the spinal bones and spinal cavity 20

Moreover, the size of these bones is not the same, nor is the foramen carrying the dorsal medulla carved out in equal size for all of them. In the interest of coordination it was better that the lesser ones be made always the higher; the one which is now supported by another should be smaller than the one bearing it. On this principle, the sacrum (G, H; or, in the complete skeletons, M with Q 21 ) was made by Nature the largest of the bones of the spine, and is placed beneath the twenty-four vertebrae as a kind of base, joined to the two largest bones (G and H), which together with it most stabilize the body. The second largest bone of the spine ascending up from the sacrum is the vertebra (F, or number 24) articulated to the sacrum, lying twenty-fourth from the first, the fifth of the lumbar vertebrae. Each of the other vertebrae differs as much in mass from the one below as it does in position. This reduction in size continues up to the head itself, except when a vertebra intervenes that is a little greater 22 than the one beneath; the description of the first vertebra [atlas] of the neck (A or 1) will show that this is not made without great usefulness. This description will explain that it is broader than the other cervical vertebrae for the convenient insertion of the fifth (I, H [musculus obliquus capitis superior] in the 14th table of muscles) and sixth (L, K [m. obliquus capitis inferior] in the same table) muscles that move the head, and the origin of the second muscle that elevates the scapulum (Q [m. levator scapulae] in the 13th table of muscles). In that passage you will hear also that for the sake of articulation the second cervical vertebra [axis] is stronger and larger than the third. Because Nature carved out the vertebrae on the posterior surface of their bodies for no purpose other than to prepare a path for the dorsal medulla (1 in the illustration preceding ch. 11, Bk. 4), it was assuredly necessary for the foramen to match the size of the dorsal medulla. And since the medulla is unequal in individual vertebrae and largest in the first ones (for it is gradually diminished and reduced by nerves put forth from it), the foramen of the upper vertebrae is rightly greater than that of the lower. Since, moreover, the upper vertebrae needed to be carved out with a large foramen and at the same time rest upon other vertebrae, it is readily deduced that they must necessarily be made thin at the same time.



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