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MANUAL OF HISTOLOGY. 



403, 404). These vary extremely in thickness, besides which one and 



the same tube may exhibit 

 at different parts of its 

 course very different dia- 

 meters. Fine lymph tubes 

 may measure 0'0361 mm., 

 or even considerably less, 

 across, whilst others show 

 a thickness two or three 

 times as great. Even in the 

 smaller mammals some may 

 be met with of 0-0902- 

 0'1263 mm. in diameter. 

 In the large lymph-nodes of 

 the ox tubular elements of 

 the medullary substance 

 may be encountered present- 

 ing a still greater diameter. 

 If we now pass on to 

 the structure of the lymph- 

 tubes, we have the most 

 striking picture presented 

 to us on rilling the blood- 

 vessels artificially; all the 

 lymph-tubes, namely, are 

 traversed by blood-vessels, 

 so that they appear like 

 lymph-sheaths around the 

 latter. According to their 

 strength, we find the axis 

 occupied by either an arterial twig, a capillary (figs. 402, a ; 403), or 



a small venous branch. If, as is the case 

 in larger animals, the lymph tubes are of 

 considerable thickness, their vascular system 

 is more complicated, as is seen in fig. 404, 

 a. Here also an arterial or venous twig 

 passes through the axis, while the peripheral 

 portion is traversed by interlacing capil- 

 laries belonging to the axial vessel and 

 forming elongated meshes. 



The tissue of the lymph-tubes is again 

 reticular connective substance ; a cellular 

 or banded network (fig. 402, >), which 

 surrounds the blood-vessels and takes the 

 place of an adventitia. 



In thick lymph-tubes also the reticular 

 character may be recognised in their in- 

 terior. The surface likewise is often ob- 

 served with the greatest distinctness to 

 have mesh-like slits. In finer tubes, as 

 also in those of the smaller animals, such 



Fig. 403. Lymph tubes (a, a) from the medullary portion of 

 the pancreas Asellii of the rabbit, with simple vessels and 

 their branches, 6, b. Between them is to be seen a strongly 

 stretched cellular network c. 



Fig. 404. From the medullary substance 

 of the inguinal gland of the ox (after 

 His), a, Lymph-tube with its com- 

 plicated system of vessels ; c, portion 

 of another; d, septa; b, retmacula 

 stretched between the tube and the 

 septa. 



as the rabbit (fig. 403, a, >), the external surface may become more or 

 less membraneous and homogeneous, resembling a hyaline glandular 



