. The cyclopædia of anatomy and physiology. Anatomy; Physiology; Zoology. VEIN. 1373 veins, the cerebral sinuses, Breschet's veins of the bones, and the venous cells of the corpora cavernosa. External coat of longitudinal fibres. — The ex- ternal coat consists of a mass of areolar tissue, adhering together with more or less compact- ness, and running in a longitudinal direction. This tunic occupies full two-thirds of the entire thickness of the whole wall of a vein. Its internal boundary is irregular at the union with the equally irregular outer limit of the middle coat, and its external bound
. The cyclopædia of anatomy and physiology. Anatomy; Physiology; Zoology. VEIN. 1373 veins, the cerebral sinuses, Breschet's veins of the bones, and the venous cells of the corpora cavernosa. External coat of longitudinal fibres. — The ex- ternal coat consists of a mass of areolar tissue, adhering together with more or less compact- ness, and running in a longitudinal direction. This tunic occupies full two-thirds of the entire thickness of the whole wall of a vein. Its internal boundary is irregular at the union with the equally irregular outer limit of the middle coat, and its external boundary is the Fig. Transverse vertical Section of Sulclavian Vein of Ox. a, internal coat; b, middle coat; c, part of external coat. (Magnified 200 diameters.) loose cellular tissue into which it degenerates, and which constitutes the "sheath" of the vessel. This coat, like the preceding, gradu- ally diminishes in density and compactness as it is examined further and further from its inner limit, though its density is everywhere inferior to that of the middle ; indeed, it may be said that the tissue of which the vessel is composed becomes looser and looser in pro- ceeding outwards from the inner boundary of the middle coat, — this quality passing gradu- ally from one coat to the other. The textural arrangement of this tunic must be examined, like the preceding, from longitudinal and transverse sections. In the former it is seen that bundles of rods of yel- low elastic tissue are disposed in alternate lamina; with white fibre, or rather, that the former are embedded in a mass of the latter, and that they are a continuation of the longi- tudinal fibres of the middle coat, which gradu- ally become arranged more and more in strata, and at increasing distances. (/YV«. 856. c.) The characters of the white fibrous tissue between the bundles of yellow, become more conspicuous as the laminae are wider apart. The stratified arrangement of the fibres, and their correspo
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