566 SPECIAL HISTOLOGY. 



substance which bounds the pulp between them. Under these circum- 

 stances we may, with perfect justice, speak of venous sinuses ; the 

 more, if we consider that these, so to say, wall-less veins have a colos- 

 sal width, and are pierced by innumerable veins which open into them. 

 These smaller veins, again, may be traced for a considerable distance 

 with the scissors, but I have as yet never been able to succeed in demon- 

 strating in what manner they are continuous with the capillary network, 

 proceeding from the penicilli arteriarum, which here also is very dis- 

 tinct. I can hardly believe that it will ever be possible to make out this 

 continuity completely, for the finest veins, which are often bounded by 

 but a few trabeculce, and indeed for the most part by the red pulp alone, 

 are such delicate canals, that the slightest mechanical force, as in in- 

 flating or injecting them, destroys them ; and even by the microscope 

 they are not discoverable. It may always be observed, however, that 

 they eventually become very minute, so small that it is impossible to 

 consider their origins as enlargements. For my own part, I believe, 

 that here also, the connection with the capillaries takes place quite in 

 the ordinary manner, with this distinction, however, that the veins in 

 arising from them possess only one membrane, an epithelium, and are 

 therefore perhaps connected in some other manner with their structureless 

 coat. Smaller series of more rounded epithelial cells, which are not 

 unfrequently found on teasing out the pulp, probably belong to the 

 smallest veins. 



In mammalia the lymphatics are stated by all authors to be extreme- 

 4y numerous, and this is perfectly true for the superficial vessels, which 

 in the Calf, for example, are exceedingly abundant and present nu- 

 merous anastomoses in the subserous cellular tissue. On the other hand, 

 I find that the deeper lymphatics are scanty. In ihe-hilus of a calf's 

 spleen, for instance, I found but four lymphatic trunks with a collective 

 diameter of 0*17 of a line. The superficial and deep lymphatics would 

 appear to be, to a certain extent, connected ; inasmuch as a few scattered 

 lymphatics, which are probably connected with those which proceed from 

 the hilus, accompany the arteries which pass from the interior of the 

 spleen, to be distributed in its coats, and open into the superficial trunks. 

 The latter may readily, in the Ox, be traced for a certain distance into 

 the interior, so far that it can be seen that they not only at first, but 

 subsequently, always accompany the arteries. Their origin is unknown, 

 and I can only say, that in the Malpighian corpuscles and in the peni- 

 cilli, as microscopic investigation shows, the arteries are no longer 

 accompanied by lymphatics. They probably, as in the liver, belong 

 only to the vascular sheaths. In structure, the splenic lymphatics 

 present no peculiarities, and they have valves. 



The arteries in, the human spleen are exceedingly muscular, which 

 sufficiently explains the dilatation and subsequent contraction of the 



