THE BLOOD-VESSELS. 303 



colour, and striped transversely. But even where thickest, 

 it is far from equalling that of the corresponding arterial vessels; 

 and in thickness never exceeds 0-06'" to 

 O07'". It consists not only of transverse , , Jf 

 but also of longitudinal layers, and in this 

 respect likewise differs from that of the 

 arteries. The transverse layers are com- 

 posed of common, undulating connective 

 tissue, with fine, loosely arranged, or rather 

 isolated elastic fibres (nucleated fibres, as 

 they are termed), and of a large quantity of smooth muscles, 

 the fusiform elements of which, 0*02 — 004"' long, and 0004 

 — 0-007"' broad, present the usual 

 characters of contractile fibre- 

 cells, whilst the longitudinal 

 laminae consist of true, thick, and 

 very thick, reticulated elastic fibres. 

 With respect to the mutual rela- 

 tions as lamina of these tissues, it 

 should be remarked that in cer- 

 tain veins (popliteal, profunda 

 femoris, saphena major and minor), 

 the /. intima is succeeded by a 

 layer, formed solely of connec- 

 tive tissue and finer elastic net- 

 works, and having a longitudi- 

 nal fibrillation — the longitudinal 

 lamina of the t. media — whilst 

 in other veins the muscular 

 elements extend also into the 

 innermost lamina. In this case, 

 immediately external to the t. intima, there is a transverse 

 layer of muscles, with connective tissue and elastic fibrils, 



Fig. 284. Transverse section of the vena saphena magna, at the malleolus, x 30 

 diara.: a, striped lamellee and epithelium of the t. intima; b, its elastic membrane; 



c, longitudinal, internal connective-tissue layer of the t. media, with elastic fibres ; 



d, transverse muscles, and e, longitudinal elastic networks, disposed in a laminated 

 manner ; /, t. adventitia. 



Fig. 285. Muscular fibre-cells from the renal vein of Man: a, without; b, with, 

 acetic acid; a, nucleus of the latter ; x 350 diam. 



