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 18 On the Sacral Bone and the Coccyx

Key to the three figures placed above and their characters

This table shows the entire structure of the dorsal bones which lie beneath the lumbar vertebrae [os sacrum et os coccygis]. The first figure, on the right, 1 shows the anterior aspect [facies pelvica] of these bones. The second, standing on the left [sic] side, shows the posterior aspect represented slightly from the side to show the depression into which the right iliac bone is articulated. The third figure, in the middle, presents the coccyx in the size and shape usually observed in persons of prime years. 2

A, B, C, D, E, F, G, H, I, K These letters in the first figure denote the nine 3 bones that come after the fifth lumbar vertebra, of which I will consider the six upper [vertebrae sacrales] 4 the sacrum in man; the four lower [vertebrae coccygeae] (G, H, I, K in the third figure) will be called the coccyx, or (as we sometimes say) the coccyx bone.
L, L, R In the first figure, the transverse processes [pars lateralis] of the bones making up the sacrum. Here, L and L

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separately mark the breadth of the process of the second bone, while R both here and in the second figure shows the tubercle of the transverse process of the fifth bone, to which you will hear several ligaments [l. sacro-iliaca, l. sacrotuberale] are attached. In the second figure, L, M, N, R mark the transverse processes of the bones of the sacrum.
N N, O O, and finally P Q F These mark the right depression [pars lateralis, facies auricularis et tuberositas sacralis] of the sacrum in the second figure, to which is connected the right ilium or (as perhaps some will prefer) the iliac bone, 5 and which later is subdivided into several depressions and protuberances. N and N mark its long anterior depression, O and O [crista sacralis lateralis] the tubercle standing out like a broad line, separating the anterior depression [facies auricularis] marked N, N from the posterior depression, marked P, F, and Q. P marks the upper cavity of the posterior depression, Q the lower, F the tubercle [tuberositas sacralis] separating the upper depression marked P from the lower one marked Q.
S In the first and second figure, S marks the right ascending process [crista processus articularis superioris] of the first bone.
T, V, X These letters appear only in the second figure. T marks the depression of the ascending process [p. articularis superior] marked S to which is articulated the tubercle 6 of the right descending process of the fifth lumbar vertebra. V and X mark the anterior and posterior brow of this depression; we have also labeled as X the inner brow of the left ascending process in the second figure.
Y In the second figure is shown the joint [articulatio zygapophysialis] that often appears by which the descending processes of the first sacral bone are joined to the ascending processes of the second, in the same fashion as you learned much earlier the lumbar vertebrae are articulated at this point.
Z In the first and second figures, the joint 7 of the transverse process of the first bone with the transverse process of the second.
a In the first and second figure, the lower, protuberant part [apex ossis sacri] of the sixth bone, which is articulated with the first bone of the coccyx.
b b In all three figures, the cartilaginous ligament [discus intervertebralis] 8 that comes between the joints of the coccyx.
c In the second and third figures, the cartilage attached to the tip of the coccyx.
d d In the second figure are shown the spines or posterior processes of the sacral bones.
e, f, g, h, i, k These letters are somewhat hidden in the second figure, marking the path [canalis sacralis] of the dorsal medulla in the sacrum and the foramina sometimes visible here among the intervals of the spines.
1, 2, 3, 4, 5, 6 These numbers in the first and second figures show the foramina [ff. sacralia anteriora et posteriora] of the nerves [rami posteriores et anteriores] beginning from the dorsal medulla contained in the sacrum; these constitute six pairs, 9 exiting in the anterior and posterior of the sacrum. The first of these [nervus lumbaris V] exits between the first bone of the sacrum and the fifth lumbar vertebra [foramen intervertebrale], and its location is marked 1. The foramen of the second pair, between the first and second bone, is marked 2, and so the rest are shown with their own numbers.

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 18 On the Sacral Bone and the Coccyx