. Journal of anatomy . ss snakes the vertebral bodies carry ribs from end to endof the vertebral column, and this completeness of the rib series is doubtless Relation of Limb Plexuses to Ribs and Vertebral Column 389 due to the fact that the nerves, instead of being gathered into plexuses forthe supply of limbs, run as bands round the body in the intervals betweenthe ribs. This complete rib series disappears with the introduction oflimbs; and it is suggested that, though other and functional factors doubt-less come into play at the same time, the gathering of the nerves into limbplexuses is th
. Journal of anatomy . ss snakes the vertebral bodies carry ribs from end to endof the vertebral column, and this completeness of the rib series is doubtless Relation of Limb Plexuses to Ribs and Vertebral Column 389 due to the fact that the nerves, instead of being gathered into plexuses forthe supply of limbs, run as bands round the body in the intervals betweenthe ribs. This complete rib series disappears with the introduction oflimbs; and it is suggested that, though other and functional factors doubt-less come into play at the same time, the gathering of the nerves into limbplexuses is the process responsible for the aljbreviation of the rib ribs are, as it were, swept from the vertebrae by the nerves convergingfrom many segments upon a central point. In order to appreciate thisfactor it is necessary to turn to the embryo (see fig. 10). In an embryo of69 mm. the nerve roots run straight to the limb buds, and between theadjacent nerve roots is the mesoblast of the somite from which the future. Fig. 10.—Diagram, after a reconstruction of anembryo of 6-9 mm., by Streeter, to show thenerve roots running to the limb plexuses. ribs are to be developed. As the length of the eml)ryo increases, theobliquity of the nerves that are gathered into the limb buds becomes pro-nounced, and with increase of growth this oblicjuity becomes more nerve, as it runs obliquely to the limb, tends to cut short the ribelement between it and its neighbour. In this way the cervical region andthe lumbar region are left ribless, for the rib rudiments are unable todevelop into the segments across which the nerves are pulled. In the dorsal region—which is essentially the region left over betweenthe segments from which limb nerves are drawn—the development of ribsmay go on uninterrupted, for here the segmental nerves run as bands, eachconfined to its owi^. segment. It is the nerves that are the dominant factors in shaping the destiniesof the future ribs, and this for
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Keywords: ., bookcentury1800, bookdecade1860, booksubjectanatomy, bookyear1867
