When the arteries have divided into small vessels of 1 to 2-100ths of a line, they come into contact with the Malpighian corpuscles in the mode already described ; while they are also connected to these by their sheaths. According to Giesker, their final terminations are coronal or pencil-shaped, radiating so as to surround the Malpighian corpuscles, and altogether enclose them ; then arriving at the highest point of the vesicle, they return upon themselves in the shape of a loop, course back again as veins, and there meet together, beneath the point whence the artery radiated, to form a vem, which enters the same sheath from which the artery emerged. At this point the sheath divides into three to four fibrous threads, which pass over on the spleen corpuscles to the threads arisin„,r nearest to them, and unite with these. If we compare with this description of the minute anatomy of the spleen that which is considered most admissible by J. Miller, the next author after Giesker, we shall find very considerable contradictions. J. Midler finds that the smallest branches of arteries partly continue on the side of the corpuscles with out giving off branches to them, partly per forate either a portion or the whole of the corpuscle, without in any instance leaving any branches of the artery in its interior ; that these fine arterial branches pass through the middle of the corpuscles, then con tinue on their coats, and then quit them altogether ; and that if an artery in the corpuscle divides into many branches—which never happens on the surface, but always in the thickness of its coats — these branches leave it again, in order to ramify minutely in the surrounding red pulpy substance of the spleen, into which part especially all the fine pencil-shaped ramifications of the arteries pass., The commencements of the veins spring from these branches; they are tolerably large, anastomose frequently with each other, and scarcely have a special coat as yet. If a little piece of the pulp of the spleen be care fully examined, it will be seen that it is as if crihriform, and constitutes as it were a net work of red partitions, the diameters of which are larger than the interspaces and canals existing between them. It is these venous canals which give the cellular appear ance seen in inflation of the veins of the pulp, and which, injected, form structures resembling the corpora cavernosa _of the penis. Special cells or cavities do not exist.
So far J. Miller. If vve now ask ourselves the reason of these important differences be tween these two authors cited, one of whom affirms the continuation of the tufts in the pulp, and a connection of Malpighian cor puscles with arteries and venous interstices only ; while the other denies all this, we shall find it not very difficult to give an answer. Giesker, in his description, limited himself to the appearances met with in the human subject, while J. 1V1iiller made the pig and the ox the basis of his delineation. This circumstance will at least partially explain the want of corre spondence in the two descriptions ; for I find that between the spleen of man and that of the animals mentioned considerable differences exist.
In man, at least generally, the arteries to gether with the veins pass deeply into the substance of the spleen, lying in the same sheath with them, and exactly following their course. According to Giesker, the two classes
of vessels accompany each other even to their final ramifications ; but this is not correct. In every spleen instances occur, which are easily seen, where small veins and arteries lie very close to each other ; and Giesker has evidently allowed himself to regard these par ticular instances as the rule, and has ex tended it as a description to the srnallest branches of vessels. But if an arterial and venous primary branch be successively fol lowed to their minutest ramifications, it will be seen that, sooner or later, every artery and vein, without exception, separate from each other, and follow their special path. It is not at all unusual to find this even with arteries from to 1 line in diameter, but it is always the case with those of from 140th of a line. In such an instance the artery, setting out alone, does not perforate the sheath in which it hitherto lay, but takes with it a distinct yet often inseparable covering of the same ; so that from this point forwards a special and se parate venous and arterial sheath exist. And in man the Malpighian corpuscles lie only on these isolated arteries ; a state which Mal pighi and Miiller had already described in Mammalia.
As regards the other circumstances of the arteries, I have found them exactly as Miiller describes them in the lower animals. After the smaller branches of the arteries are connected with the Malpighian corpuscles, they enter into the red spleen substance, and immediately upon this each small trunk spreads out in the shape of a tuft into a large number of yet finer arte ries (fig. 526, d.); and these tufts or pencils of arteries, lying in great nurnbers close to each other, give to the terminations of the arterial trunks a very beautiful appearance, which may be best compared to the broad crown of a (pollard) tree. These separate tufts, dividing and diminishing in size yet more, terminate by an immediate transition into the true capillaries ; which, in a more and most minute form of 3 to 5-1000ths of a lirie, constitute a close and beautiful network in the separate portions of the pulp, and in those parts of it which sur round the Malpighian corpuscles ; although they do not form a special vascular covering for the same. Many authors seem to deny the existence of capillaries in the spleen : thus Engel* has lately altogether denied them ; but this is quite erroneous. They may easily be seen in the pulp of the human spleen, by the aid of the microscope, both empty and filled with blood, and exhibit themselves as in no way different from the capillaries of other organs ; and the finest of them have a dia meter of only 3-1000ths of a line. J. Miller is also in error when he describes the arteries as coursing through the coats of the Mal pighian corpuscle, since they always pass on its exterior. Finally, Giesker is wrong in describing the arterial pencils as spreading themselves out on the Malpighian corpuscle, and here becoming continuous with the veins ; even in man it is not difficult to discover that the pencils only begin beyond the corpuscles, that they lie in the pulp, and that it is here they first break up into capillaries.