. The cyclopædia of anatomy and physiology. Anatomy; Physiology; Zoology. 1388 VEIN. spaces : — these anastomoses being all on the same plane, excelling at a few points here and there where a small channel clips down to the devp veins. Such plexuses may be seen on the dorsinn of the hand and foot. But the most elaborate and complex of all the plexuses in the human* subject are those formed around, about, and within, the spinal canal: they are composed of nu- merous trunks, which unite, divide, and re- Fig. Plexuses connected with the Spinal Canal. a, the great anterior spinal veins (t\\e
. The cyclopædia of anatomy and physiology. Anatomy; Physiology; Zoology. 1388 VEIN. spaces : — these anastomoses being all on the same plane, excelling at a few points here and there where a small channel clips down to the devp veins. Such plexuses may be seen on the dorsinn of the hand and foot. But the most elaborate and complex of all the plexuses in the human* subject are those formed around, about, and within, the spinal canal: they are composed of nu- merous trunks, which unite, divide, and re- Fig. Plexuses connected with the Spinal Canal. a, the great anterior spinal veins (t\\e"grandesveinesrachidiennes longitudinales anterieures"of,~Breschet) ; b, ascending lumbar veins (the "veines lombaires ascendantes" of Breschet) ; c, veins uniting the above- mentioned, through the intervertebral foramina (after Breschet). unite, at every possible point, and in all con- ceivable modes, by branches of all sizes, lengths, and shapes, and leave intervals pre- senting forms of endless variety. A portion of these plexuses, seen in the accompanying figure, from Breschet's work on the veins, conveys a better idea of them than any lengthened description. The dlploic plexuses are the net-works of veins which exist in and among the cancel- lated tissue of the bones. In the flat bones of the cranium, at the period of adult life, they form large irregular meshes, by the mean- derings of large, irregular, ampullated, veins. These vessels are very unequal in size, are subject to dilatations, and frequently end in culs-de-sac. They are well represented in figs. 187. and 188. Vol. I. But the most re- markable peculiarity in these plexuses, is the change they undergo during osseous de- velopment. In early foetal life, when ossifi- cation commences the cranial bones consist of stellfE of numerous ossific rays, the inter- spaces between them being occupied by hosts of small, almost straight, radiating, veins: these veins are not covered in by osseous struct
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