THE SPLEEN. 565 



that, taken together, they equal the empty and collapsed splenic artery, 

 this size, however, heing attributable principally to the unusual quantity 

 of Remak's fibres. 



In animals, these nerves, which never possess ganglia, may be followed 

 into the spleen further than in Man; and, by the aid of the microscope, 

 I have frequently met with them even upon the arteries which support 

 the splenic corpuscles. As to their terminations, I can only state that 

 they pass into the pulp, and are still to be met with upon the arterial 

 penicilti. Here they ultimately become as delicate as the finest capilla- 

 ries, no longer possess dark-edged tubules, and, according to Ecker's 

 observations (1. c., p. 149, Fig. 10), probably end in free dichotomous 

 divisions. In the Calf, the nerves upon arteries of 1 line measure 

 0-024-0-028, on the penicilli artertarum 0-0048-0-0056, in the midst 

 of the pulp 0-003-0-004 of a line. In branches of 0-012-0-028 of 

 a line, I here still found a single dark-edged nerve-tubule, whilst all 

 the rest consisted of a striated nucleated tissue, which alone consti- 

 tuted the finer threads. It is improbable that this structure has here, 

 as in the trunks, the import of Remak's fibres ; I should rather with 

 Ecker, consider it to be embryonic nervous tissue, such as we are 

 sufficiently acquainted with in other localities; and I 'am inclined to 

 believe that the dark-edged tubules of the trunks finally pass into pale 

 fibres, as such compose entirely or almost entirely the ultimate twigs, 

 and then terminate by branching out. In the trunks of the splenic 

 nerves of the Calf, there are found, before their entrance into the spleen 

 and within it, numerous dichotomous divisions of the dark-edged, partly-* 

 coarser and partly finer primitive tubules, such as I have not hitherto 

 succeeded in detecting in Man. 



In regard to the structure of the veins, many of the Mammalia ap- 

 pear to resemble Man, while others, as the Horse, Ox, Sheep, Pig, pre- 

 sent very wide differences. In these animals a special venous membrane 

 and a vascular sheath are found only at the origins of the largest 

 venous trunks, while further in, they are visible only upon the side of 

 the arteries. In all the smaller veins, which run independently (with- 

 out arteries), no further trace of two coats is to be met with, in fact, 

 these veins appear to be mere excavations in the substance of the spleen, 

 especially as a number of anastomosing trabeculce with red pulp often 

 forming projecting knobs between them, are apparent upon their walls. 

 However, they always have a perfectly smooth and shining surface, 

 arising from spindle-shaped, tessellated epithelium-cells of 0-005-0-01 of 

 a line, which are only microscopically demonstrable. This epithelium cor- 

 responds perfectly with that of the larger veins, only that here it no 

 longer lies upon a special wall, but immediately upon, the substance of 

 the spleen, i. e. upon the trabeculce and upon a delicate membranous 



