Abstract
THE almost absolute rule that there are seven true ribs in the human subject has, like every other rule, its exceptions. Occasionally instances are met with in which there are eight sternal ribs on one or both sides. But Nature does not effect her evolutions by per saltum transitions between extreme points, but steadily makes progress by degrees almost imperceptible to human intelligence. So in the matter of rib transition, there are various grades met with between the presence of a complete eighth sternal rib on the one hand, and its absence on the other. In the sternum of a female subject recently dissected at the Royal College of Surgeons, the right seventh and eighth rib cartilages blended together about a quarter of an inch distant from the mesosternum. On the left side the eighth rib cartilage was arrested about an inch and a half from the mesosternum. The latter was free at its sternal end. In another subject—a moderately muscular male—the eighth rib cartilage on the right side extended within an inch of the mesosternum, its extremity being free. On the left it was aborted at the distance of two and a half inches from the mesosternum. In the latter subject the sternum was exceedingly large; all the rib cartilages, especially the seventh on the left side, were well developed, and the xiphisternum was very much elongated, spatulate, and curved in an anterior direction. Occasionally specimens are met with in which the sixth rib cartilage is implanted upon the distal extremity of the mesosternum (rather than upon its distal lateral aspect), lying in front of the xiphisternum, and separated from its fellow of the opposite side by a small interval. In the receding angle formed by their divergence, the seventh sternal ribs are placed, lying directly upon the xiphisternum, and articulating with it, barely attaining an attachment to the mesosternum. This closely simulates the arrangement met with when the eighth sternal rib is present.
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BESWICK-PERRIN, J. On an Additional True Rib in the Human Subject . Nature 4, 188–189 (1871). https://doi.org/10.1038/004188a0
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DOI: https://doi.org/10.1038/004188a0