686 



SPECIAL HISTOLOGY. 



. 285. 



termed), and a large quantity of smooth muscles, the fusiform elements 



of which, 0-02-0-04 of a line long, 

 and 0-004-0-007 broad, present the 

 usual characters of contractile fibre- 

 cells, whilst the longitudinal lamince 

 consist of true, thick, and very thick, 

 reticulated elastic fibres. With respect 

 to the mutual relations as lamince 

 of these tissues, it should be remark- 

 ed that in certain veins (popliteal, 

 profunda femoris, saphena major and 

 minor), the t. intima is succeeded by 

 a layer, formed solely of connective 

 tissue and finer elastic networks, and 

 having a longitudinal fibrillation the 

 longitudinal lamina of the t. media 

 whilst in other veins the muscular ele- 

 ments extend also into the innermost 

 lamina. In this case, immediately 

 external to the t. intima, there is a 

 transverse layer of muscles, with con- 

 nective tissue and elastic fibrils, which three tissues, in these veins, 

 always accompany each other ; to this succeeds a regular alternation of 

 longitudinal, elastic, reticulated membranes, always in a single layer, 

 and transverse muscles with connective tissue, so that the t. media of 

 these veins presents a laminated aspect, somewhat resembling that of 

 the largest arteries. It should, however, be remarked, that the elastic, 

 reticulated membranes, although frequently very closely interwoven, 

 nevertheless never form homogeneous, elastic membranes ; moreover, 

 that they are occasionally interrupted, and, as longitudinal sections 

 manifestly show, are invariably continuous with one another through 

 the whole t. media. The number of these elastic lamella? fluctuates 

 between five and ten, and their interspaces vary in width from 0-004- 

 0-01 of a line. The t. intima of the medium-sized veins is 0-01-0-04 of 

 a line thick, and consists, where it is thinner, only of an epithelium with 

 shorter, though elongated cells, a striated, nucleated lamella, and an 

 elastic longitudinal membrane, corresponding to the elastic inner mem- 

 brane of the arteries, but which scarcely ever appears as a truly homo- 

 geneous, fenestrated membrane, but most usually as an extremely close, 

 areolated network of finer and coarser elastic fibrils. Where the t. 

 intima is thicker, the striated lamella? are multiplied, and, above all, one 

 or even several additional networks of elastic, fine fibres make their ap- 



FiG. 285. Muscular fibre-cells from the renal vein of Man ; a, without ; 6, with acetic 

 acid; a, nucleus of the latter. Magnified 350 diameters. 



