314 SPECIAL HISTOLOGY. 



tunics. The /. intima consists of an epithelium, of elongated, 

 although rather short cells, and of a single, rarely double elastic 

 reticulated membrane, longitudinally fibrillated, which, as regards 

 the thickness of its fibres, and the narrowness of the meshes, 

 exhibits manifold diversities ; but it never has thick fibres, nor 

 does it ever constitute a true elastic membrane (according to 

 Weyrich, this membrane is wanting in the lymphatics of the 

 mesentery, whilst I have always found it in those of the lumbar 

 plexus, and in those of the extremities). This is succeeded by a 

 stronger, t. media, composed of transverse smooth muscles, with 

 fine, also transverse elastic fibres ; and lastly, there is a t. adven- 

 titia, with longitudinal smooth-muscular fasciculi. The latter I 

 have found, in the extremities, upon vessels of not more than ^", 

 and I consider them a good distinctive character between lym- 

 phatics and small veins (vid. Mikrosk. Anat., II, p. 236). 



The thoracic duct differs in some respects from the smaller 

 lymphatics. The similarly constituted epithelium is succeeded 

 F 289 ky some striped lamella, and these by an 



elastic reticular membrane, longitudinally fibril- 

 lated, although the entire t. intima scarcely 

 measures 0006 — 001'". The t. media, 0-025'" 

 thick, commences with an extremely thin 

 layer of longitudinal connective tissue, with 

 fine elastic fibres, and consists, besides, of a 

 transverse muscular layer, with fine elastic fibres. The t. adven- 

 titia, lastly, contains longitudinal connective tissue, together 

 with elastic fibrils, and a few reticularly connected bundles of 

 longitudinal muscles. The valves of this duct, and of the lym- 

 phatics in general, correspond completely with those of the veins. 

 The blood-vessels of the lymphatics present the same con- 

 ditions in the thoracic duct as in the veins. No nerves have 

 been found in them. 



§ 219. 



Lymphatic glands. — These glands [glandula lymphatics) 

 differ very considerably from the rest of the blood- vascular 



Fig. 289. Transverse section of the thoracic duct in Man, x 30 diam.: a, epithe- 

 lium, striped lamellce, and elastic inner membrane; b, longitudinal connective tissue 

 of the t. media ; c, transverse muscles of the same tunic ; d, t. adventitia, with e, the 

 longitudinal muscles. 



