. The cyclopædia of anatomy and physiology. Anatomy; Physiology; Zoology. Diploic Veins in a Vertebra. a, great anterior spinal veins; b, posterior spinal veins ; c, transverse branches ; d, venie basis ver- tebrarum; e, vein on the surface of the body of the vertebra. (After fJreschet.) FiS. 87?.. Parietal Bone of Foetus at nine months, exhibiting the veins. (After Breschet.} IV. FUNCTION OF VEINS. — In function veins may be considered as having a triple office : they are passive organs of circulation; they are diverticnla or reservoirs for blood ; and they are agents of absorption. Circulati
. The cyclopædia of anatomy and physiology. Anatomy; Physiology; Zoology. Diploic Veins in a Vertebra. a, great anterior spinal veins; b, posterior spinal veins ; c, transverse branches ; d, venie basis ver- tebrarum; e, vein on the surface of the body of the vertebra. (After fJreschet.) FiS. 87?.. Parietal Bone of Foetus at nine months, exhibiting the veins. (After Breschet.} IV. FUNCTION OF VEINS. — In function veins may be considered as having a triple office : they are passive organs of circulation; they are diverticnla or reservoirs for blood ; and they are agents of absorption. Circulation in the veins consists of the passive and equable transmission of blood along their tubes. " When we consider the great size of the veins, compared with the arteries, we must conclude that the blood flows but slowly in the venous system ; that, from the narrowness of the trunks of the veins near the heart, the blood must be ac- celerated as it approaches the heart ; and that receiving the impulse from the ventricle, it must take a rapid course through the arteries, until, again approaching the extreme branches of the arteries, and passing into the veins, its motion becomes more languid and slow. In youth, as the size of the veins is not in so great a proportion to the arteries as in advanced life, the blood must be in more rapid circulation : but in old age, owing to tlie largeness of the veins and the accu- mulation of blood in them, it moves slowly through the venous system, and is almost stagnant in the dilated veins and in the sinuses. " There is no pulsation to be observed in the veins, but what they receive from con- tiguous arteries. There is no pulsation in the veins because they are removed from the heart ; because they do not receive the shock of the heart's action in their trunk, but only by their widely-spread branches ; because the contraction of the heart and of the arteries so alternate with each other, as to keep up a perpetual and uniform stream
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