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

Description of the simian and canine sacrum

In dogs and apes, a certain bone [os sacrum] composed of three bones [vertebrae] is located beneath the lowest lumbar vertebra (nos. 1, 2, 3 in fig. 4; I have placed no further markings on this figure because the human bone is fully marked and it will be explicated later). These are so joined that in front [facies pelvica] near their middle they show the same kind of joint as the bodies of vertebrae would display when fitted together, if they ever came together in such a way that they could not be moved even a little, and all cartilage had disappeared from between them over the passage of time 21 —though in puppies even the union of sacral bones is seen to be filled with a certain amount of cartilage (as in the connection of the epiphyses). In the sides of the anterior place just mentioned, these bones show hardly any appearance of a joint when the animals are old, but appear to have been solid from the beginning, just as the posterior side of these very bones seems quite solid (except perhaps in very young puppies). These three bones joined in this fashion are called the sacrum or large, wide bone by Galen in De ossibus and De anatomicis administrationibus. 22 These bones are laterally broad and continuous, and while they somewhat resemble vertebrae, they form here large, wide transverse processes which join together and have cut into them a conspicuous, uneven, and rough depression [facies auricularis] on their outer side (fig. 5 shows this on each side) by which the ilium is quite firmly attached to the bones. In the posterior part, this bone forms three slender spines [crista sacralis mediana], less upwardly inclined than Galen thought, and constituted throughout like a continuous line. Above and below, this sacrum corresponds to a large degree to the lumbar vertebrae: the upper part resembles their superior surface and the lower resembles the inferior. The upper part of the sacrum [basis ossis sacri] has an epiphysis [processus articularis superior] and protrudes with the same mass as the lower part of the body of the lowest lumbar vertebra [processus articularis inferior], which is joined to the sacrum in exactly the same way as the lumbar vertebrae are joined together. In addition,


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the upper part of the sacrum puts forth two ascending processes, having depressions like the ones with which we stated the ascending processes of the lumbar vertebrae are engraved. The tubercles of the descending processes of the lowest lumbar vertebra are received by these. In addition, the inferior part of the sacrum (which is the lower surface of the third and narrowest of the three bones of the sacrum) also protrudes with a rounded body [cornu sacrale?] quite similar in shape to the bodies of the lumbar vertebrae. It differs from these in no way except that the body of the sacrum is as much smaller than the bodies of the lumbar vertebrae as its body’s mass is smaller than theirs. This body of the sacrum is joined to a single ossicle [vertebra] (no. 4 in fig. four) which will now be described first of the three bones of the coccyx.



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