THE LYMPHATICS. 695 



extremely thin layer of longitudinal connective tissue, with fine elastic 

 fibres, and consists, besides, of a transverse muscular layer, with 

 fine clastic fibres. The t. adventitia lastly, contains j,;^ ogg 



longitudinal connective tissue, together with clastic 

 fibrils, and a few reticularly connected bundles of lon- 

 gitudinal muscles. The valves of this duct, and of 

 the lymphatics in general, correspond completely with 

 those of the veins. 



The bloodvessels of the lymphatics present the same " 

 conditions in the thoracic duct as in the veins. No nerves have been 

 found in them. 



> 



§ 219. Lympliatic glands. — These glands [glandulce lympliatiecc) differ 

 very considerably from the rest of the blood-vascular glands Avith which 

 they are usually classed, and approach nearest to the Peyerian patches 

 of the intestine, although they do not vrholly correspond with them. 

 Every normal lymphatic gland, within a thin but tough sheath^ com- 

 posed of nucleated connective tissue and fine elastic fibrils, presents a 

 soft, whitish-red parenchyma, in which three elements, viz. a fibrous 

 tissue, a soft, pultaceous j^ulp, and bloodvessels, are manifest. The 

 fibrous tissue, formed partly of fibrous, and in part of more homoge- 

 neous connective tissue, Avith scattered fine elastic fibres, when the 

 gland is well developed, as is not always the case in Man, but almost 

 invariably in the Cat, Dog, Rabbit, Rat, &c., presents a large number 

 of thin (0*004-0-005 of a line and more) lamelloi arising from the 

 sheath, which are so regularly connected together as to constitute an 

 elegant areolated structure pervading the entire gland, all of whose 

 roundish spaces, ^-|- of a line wide, openly communicate, it is true, 

 with each other, but much less freely than is the case with the cells of 

 the corpora cavernosa, for instance. Now, since all these spaces are 

 occupied by the grayish-white pulp, the entire gland exhibits externally, 

 and, in some degree, also in a transverse section, a coarsely granular, 

 vesicular aspect, which was known even to the older anatomists, almost 

 like that of the Peyerian patches, since there may be distinguished in 

 it a great number of clear round bodies, like follicles, surrounded by 

 narrow, somewhat darker borders. But upon proceeding to isolate 

 these bodies we shall fail in the attempt, and the septa by which they 

 are parted will be found to be always common to several, something 

 like the walls of the alveoli in the adult lung. Consequently, notwith- 

 standing the similarity in outward appearance, and as we shall find, in 

 contents also, there is a very essential difference between the follicles of 



Fig. 2S9. — Transverse section of tlie thoracic duct in Man, magnified 30 diameters : 

 a, epithelium, striped lameUce, and elastic inner membrane ; 6, longitudinal connecti%'e tissue 

 of the t. media; c, transverse muscles of the same tunic; d, t. advcnlilia, with c, the longitu- 

 dinal muscles. 



