SPLEEN. 



791 



leave the arteries and pursue their way alone, 

 they vary in some respects from this descrip- 

 tion, although not so considerably as might be 

 imagined from the delineations which have 

 been given of them. In the first place, the 

 character of the branchings is peculiar, since 

 from hence onwards, and so much the more 

 frequently the smaller the veins become, 

 brandies are given off from the veins on all 

 sides at very nearly right angles, and the open 

 mouths of these ramifications are seen from 

 within as numerous round or oval orifices 

 lying very closely to each other. In the 

 second place, the membranes of these veins 

 gradually become thinner and thinner, and at 

 the same time are blended with the similarly 

 attenuated sheaths, so that both constitute 

 only one delicate membrane, which is never- 

 theless everywhere demonstrable even in the 

 smallest vessels which can be isolated, and 

 which everywhere exhibits itself without any 

 interruption as a perfectly continuous mem- 

 brane. Dilatations or pouchings can no- 

 where be seen, either in the course of the 

 isolated veins or in their smallest branches ; 

 only it must be added, that the narrowing of 

 their calibre occurs much more slowly than in 

 the arteries. As to the beginnings of the 

 veins, and their connection with the ca- 

 pillaries. I have not been able to detect any- 

 thing more than what one sees elsewhere ; 

 namely, that by a constant simplification and 

 attenuation of their structure, the veins finally 

 pass into capillaries. Here also no traces of 

 dilatations are visible, of whatever kind these 

 dilatations might be imagined to be ; and there 

 is just as little appearance of any other pecu- 

 liarity. 



As regards the brute mammalia, many of them 

 certainly correspond in a very considerable de- 

 gree with man, in respect of the condition of 

 these vessels ; but my researches do not ex- 

 tend sufficiently to enable me to express myself 

 decisively on this point. While, on the other 

 hand, some, as the horse, ass, ox, pig, and 

 sheep, exhibit essential differences. In the 

 latter animal, which I have examined the most 

 carefully, the following deviations are pre- 

 sent. The arteries differ little from those of 

 man, only they separate earlier from the veins 

 to pursue their isolated course. In most 

 other respects they behav% precisely as J. 

 Miiller has described them, and as I have 

 also spoken of them in man ; only I cannot 

 corroborate the statement of Miiller, that the 

 sheaths of the smaller arteries are equal in 

 strength to those of the greater. The rami- 

 fications which reach the Malpighian cor- 

 puscles measure from 1 to |i--10()ths ofaline in 

 diameter; they then course in the pulp, form 

 very beautiful tufts, and finally capillaries, of 

 which the smallest measure from 3 to 4- 

 lOOOths of a line. But in contrast to this, the 

 veins exhibit very essential differences. In 

 the first place, a special membrane and sheath 

 are only found in the largest venous trunks, 

 and even here they only extend a short dis- 

 tance around the circumference of the vessel ; 

 while more deeply in the spleen they only lie 



upon the side where the artery and nerve are 

 attached to the vein. In all the smaller veins 

 which are no longer accompanied by arteries, 

 there is no trace of these two membranes to 

 be seen ; and not only is this the case, but 

 the mode in which the precise limit of the 

 venous canal is indicated is also very extra- 

 ordinary. The vein appears to be formed in 

 the first instance by the strong anastomosiiv 

 trabeculae, and soon afterwards it seems com- 

 posed simply of delicate fibres and red sub- 

 stance deposited between them, a structure 

 which continues even into the large venous 

 trunks. They thus distinguish themselves at 

 the first glance as excavations in the paren- 

 chyma of the spleen, which are devoid of 

 walls. Nevertheless, by a more careful ex- 

 amination of the red limits of these veins, one 

 may verify their smooth and shining appear- 

 ances, a circumstance which is significant of 

 the existence of a delicate membranous cover- 

 ing ; and, in point of fact, microscopic inves- 

 tigation proves the existence of an epithe- 



F: g . 534. 



Epithelial cells from the Splenic vein of Man and 

 other Mammalia. Maynijitnl 350 diameters. 



lium, which every where clothes this surface, 

 and consists of fusiform or more spherical 

 cells, of * to l-100th ofaline in diameter, with 

 roundish or elongated nuclei of 3 to 5- 

 lOOOths of a line in size (Jig. 534-.). This epi- 

 thelium altogether corresponds with that which 

 covers the part of the veins possessing a 

 visible membrane ; but in the vessels of which 

 I am speaking, it is placed in part imme- 

 diately on the trabeculae, in part upon a deli- 

 cate fibrous membrane limiting that part of 

 the pulp which bounds the veins. In con- 

 sequence of what has been said, the greater 

 number of the splenic veins of (he ox must be 

 likened in respect of their structure to the 

 spaces in the corpora cuvernosa penis, and to 

 the sinuses of the dura mater ; since, in- 

 stead of the venous membranes elsewhere 

 present, they possess only the " tunica iiitima " 

 in the shape of a delicate epithelium. >So that 

 one may speak of them as " venous sinuses," 

 and the more correctly, if it be considered 

 that these veins, almost devoid of walls, 

 possess a colossal width, and are every- 

 where rendered quite cribriform by larger and 

 smaller veins opening into their interior ; 

 which smaller veins may themselves be traced 

 by their great width for a considerable dis- 

 tance. How these smaller veins are con- 

 nected with the very distinct capillary net- 



3 E -i 



