. The cyclopædia of anatomy and physiology. Anatomy; Physiology; Zoology. VEIN. 1375 cular tunic is less distinct, thinner than the areolar, with which it is more or less mixed up, and the latter is more abundant and more developed than in small arteries. In passing to vessels of larger size, the fibrous tissue is seen to have a more conspi- cuous development. The longitudinal stri- Fig. A, Small Portion of the Margin of a compressed specimen of the Renal Vein of a Rabbit, treated with Acetic Acid. a, external longitudinal coat, exhibiting yellow fibres and persistent nuclei of areolar t
. The cyclopædia of anatomy and physiology. Anatomy; Physiology; Zoology. VEIN. 1375 cular tunic is less distinct, thinner than the areolar, with which it is more or less mixed up, and the latter is more abundant and more developed than in small arteries. In passing to vessels of larger size, the fibrous tissue is seen to have a more conspi- cuous development. The longitudinal stri- Fig. A, Small Portion of the Margin of a compressed specimen of the Renal Vein of a Rabbit, treated with Acetic Acid. a, external longitudinal coat, exhibiting yellow fibres and persistent nuclei of areolar tissue; b, middle circular tunic, showing nuclei of muscle cells ; c, internal longitudinal coat (striated mem- brane), the limit of the vessel's cavity; d, corre- sponds to a small portion of the cavity of the vein. B, Ulinitte Vein from Mesentery of Rabbit, exhibit- iif/ the three Tunics Jess ; (Magnified '200 diameters.) ations and fibres on the lining membrane form a perfect striated membrane, and, in still larger vessels, increase so as to constitute a compact coat of fibres, of more or less density — the internal tunic of longitudinal fibres. In the middle coat, the muscular element becomes involved and mixed up with areolar tissue, some fibres of which run parallel, and some at right angles to tiie muscular nuclei. The external tunic of areolar tissue becomes in- creasingly developed, and yellow fibrous tissue conspicuous and abundant.* In fg. 8GO. A, is represented part of the renal vein of a rabbit. The vessel is not cut open or seen in section, but is simply laid upon, glass, treated with acetic acid, and a small portion of the margin submitted to mi- croscopical scrutiny- The internal membrane is densely striated, and the other coats de- veloped in proportion. * In the comparative examination of small and large blood vessels, there is much to confirm Henle's doctrine of nuclear and celt fibre. In the capillaries, which are mere tubular cells, there
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