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

Varieties of the spine

Nature granted to all the thoracic vertebrae a spine that is single over its entire course and not at all forked (c and ϖ in fig. 8, ch. 15). The shape of this spine does not look the same in all vertebrae. The nine upper vertebrae put forth the longest spines (N, O, P in figures 1 and 2), not very broad but narrowing gradually to a point from a broad base and resembling a triangle just as if they consisted of a triangular pyramid. For on their upper surface they present a straight, sharp line extending longitudinally (N in figure 2); they have a similar line along each side next to their lower surface (O and P in figures 1 and 2), so that the three long, sharp lines of a single spine form three surfaces, two of which (from O to N and from N to P in figure 2) constitute the upper portion of the spine 35 facing the vertebra above; there is one of these on each side. The third surface (between O and P in figure 1) is the lower portion [Q], overhanging the spine of the vertebra beneath. These three surfaces in the same spine are observed in the nine superior vertebrae, more or less identical and equally broad. Two of their surfaces are quite smooth, but the third, lower one is rough, and divided by a kind of line (Q in fig. 1) running along its longitude. From this line on the third surface comes a ligament [ll. interspinalia] that is inserted in the line common to the two surfaces; binding the spines to each other and filling the interval between them, it separates the right muscles of the spine from the left, corresponding to the ligament [membrana interossea] that I will explain lies between the ulna and the radius (a between E and I in fig. 1, ch. 1, Bk. 2) and between the tibia and the fibula 36 (S, T, V in the 7th table of muscles). Sometimes the upper surfaces appear broader than the lower one, and the spines themselves are more laterally depressed (as is observed in quadrupeds). The tenth thoracic vertebra puts forth a spine that is not as prominent as the upper ones, and does not present


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that triangular look as perfectly because the two upper surfaces are rather broad. The third or lower surface is narrow and not very depressed, but noticeably rough and uneven. The point of this spine is wide and blunt, not narrow and sharp like the spines of the higher vertebrae. The spine of the eleventh vertebra (R in fig. 3) extends still less than that of the tenth, is more depressed on both sides, and (if you look above and below it) 37 more broadly shaped. Its lower surface swells noticeably into a line and is no longer depressed 38 but rough and compact; the point of this spine is quite blunt and thick. The spine of the twelfth (S in fig. 4) differs still more from those of the upper vertebrae, substantially resembling the spines of the lumbar vertebrae (C, D, E, F, G in fig. 2, ch. 17), which are quite depressed on each side and, if you look at the top and bottom, quite broad and bulky. And just as the spine does not have the same shape in all the vertebrae, so too the spines differ from each other in their course (see the fig. in ch. 14 and skeletons 2 and 3).



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