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 19 On the Bones of the Thorax

Description of the human pectoral bone

But if you had studied the human pectoral bone (all of figs. 6 and 7) (which is in general broad, though by far the shortest if compared with the bones of other animals), you would notice that it is much different. 58 For I can affirm with certainty that I have never found seven bones in the human pectoral bone, 59 nor in man are these bones always found in the same number. In adults, about three are seen, quite different from each other. The first [manubrium sterni] is remarkably wide (g to h in fig. 1, and in 6 and 7 from s to t) and also rather thick, but only to the degree that its thickness is greatly exceeded by its breadth. On its inner or posterior surface (o in fig. 7) where it faces the cavity of the thorax, this bone is slightly concave; on the anterior it is convex, and much thicker in the middle lengthwise than at its sides, for it is depressed on the sides of its anterior surface and made thin to match the thickness of the cartilage of the first rib (p in figs. 6 and 7) [incisura cartilaginis costalis I]. In the middle, though, it protrudes in a triangular shape (q, r, l in fig. 6) for strength. The upper part of the bone (p, q, s, r in figs. 6 and 7) is much thicker and broader than the lower (t, u in figs. 6 and 7), and has on each side a single long depression [incisura clavicularis] (q, r in figs. 6 and 7) cut towards the posterior and lined with cartilage: to this the head [extremitas sternalis] of the clavicle (A in fig. 1, ch. 22) is articulated. Between these depressions, because of their swelling inner sides, this first bone is lunate (s in figs. 6 and 7) in this upper surface and shows a kind of fovea [incisura jugularis] which we properly call sfagh/ and iugulum, “throat,” and laymen the upper fork. 60 The lower part of the bone (t in figs. 6 and 7) is quite rough and is so loosely attached by cartilaginous ligament 61 to the second bone [corpus sterni], which I shall now describe, that the connection of these bones never goes unnoticed, and its motion is sometimes actually perceived during deep breathing. The second bone (from h to i in fig. 1) is much wider than it is thick, and denser on its upper surface where it is attached to the first bone (t in figs. 6 and 7) than it is near the bottom (near e in fig. 6). But nowhere is it as wide as the upper part of the first bone. At the point where this second bone is joined to the first, a bluntly angled depression [incisura cartilaginis costalis II] (u in figs. 6 and 7) is carved on either side of the joint, common to both bones and lined with cartilage; to this the cartilage of the second rib (D in fig. 1), protruding like the tip of a rather blunt triangle, is articulated. Besides this depression, the present bone forms many others [incisurae cartilaginis costalis] (x, y, z, a, b in figs. 6, 7) on each side in a similar manner, pushed in at a blunt angle; these are separated at not at all uniform intervals. The first depression [incisura] on each side belonging to this bone, made for the cartilage of the third rib, is farther from the depression incised for the second rib than from the second depression peculiar to this bone, carved for the fourth rib. 62 Again, a greater interval stands between the second depression and the third than between the third and the fourth, so that the depressions carved in this bone for the sixth and seventh ribs adjoin each other and are scarcely separated; 63 they are also not so deeply excavated as the higher ones. This second bone by itself receives the cartilages of the third, fourth, fifth, sixth, and seventh ribs which protrude like the cartilage of the second rib (E in fig. 3). In children, it is seen to have been formed from several bones (g, d, e in fig. 6) knit together by the symphysis or fusion of cartilage. But this knitting-together 64 is never comparable to an ape’s or a dog’s structure of bones, since it is much harder to see and the lower bones are much shorter than the upper. In cemeteries the second bone is almost always unearthed in one piece and separate from the first, just as the vertebrae are brought up separated from each other, although by chance you will observe another type of structure in the second bone, as if it was made of several bones. This will most often appear where the cartilage of the third rib is articulated to the bone (g in fig. 6) 65 , and next often where the cartilages of the fourth ribs are joined into the pectoral bone (d in fig. 6) 66 . Now the third bone [processus xyphoideus] (from i to k in fig. 1, z in figs. 6 and 7) is scanty, and is joined to the inner part of the lower surface of the second bone by the same method 67 as it has been explained the first is joined to the second; it is joined to the second bone where the cartilages of the seventh ribs are articulated to the lowest part of the second bone 68 . This bone is moderately wide and thin, and in its lower portion it reverts into a pointed cartilage. 69



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 19 On the Bones of the Thorax