352 EPITHELIAL AND ENDOTHELIAL TISSUE. 



terminal branches, which produce delicate capillaries for the 

 supply of the connective-tissue septa and for the pulp-cords. 

 The veins arise from these capillaries, and represent vessels with 

 thin endothelial walls, susceptible of a high degree of dilatation 

 (Billroth). These vessels traverse the interstices between the 

 pulp-cords and the connective-tissue trabeculae, and produce 

 tassel-like formations, which finally collect into larger veins. A 

 number of observers maintain that the arterial capillaries are 

 directly connected with the capillary veins j that therefore the 

 vascular system of the spleen is closed everywhere. Wedl even 

 admits a direct communication between arteries and veins. Others 

 believe in the presence of lacunae, destitute of walls of their own, 

 interposed between the terminating capillaries of the arteries and 

 the roots of the veins. The latter view is not sufficiently sup- 

 ported, for the walls of the capillaries of the spleen, as well as 

 those of lymph-ganglia, are* easily permeable to stained liquids 

 injected from without. The important question as to the termi- 

 nation and origin of the capillaries is unsettled. 



The origin of the lymph- vessels is also a much-discussed ques- 

 tion. Tomsa considers the lacunas as the roots of the lymphatics, 

 because he succeeded in injecting them through the lymphatics. 

 Probably the relations' are the same as in the lymph-ganglia. 

 Besides the lymphatics of the pulp, there are others in the cap- 

 sule, and Wedl found in the spleen of the horse and the sheep 

 two layers, the superficial being composed of narrow capillaries 

 and wide meshes, the deeper of large, sinus-like capillaries, freely 

 anastomosing with each other. 



The manner in which nerves terminate in the lymph-ganglia 

 and in the spleen is unknown. 



I have thus briefly presented the views of other observers, 

 because, on account of the lack of personal researches, I have no 

 positive knowledge concerning the structure of the lymph-ganglia 

 and the spleen. 



