788 



SPLEEN. 



in one line upon each other in the gastro- 

 splenic omentum, and they are also connected 

 to each other by fat and areolar tissue. The 

 size of the splenic arteries is very consi- 

 derable in proportion to that of the organ, 

 and so also the thickness of their coats is 

 worthy of notice. In the first of these re- 

 spects, it is possible that only the thyroid 

 gland exceeds the spleen ; the liver, which 

 is so much larger than this organ, being sup- 

 plied by an artery of scarcely larger size 

 than the splenic, although we must not over- 

 look the fact, that beside this the liver receives 

 very much additional blood through the vena 

 portae. In the mammalia generally, the splenic 

 artery is proportionally smaller than in men ; 

 this possibly depends only upon the more 

 considerable contraction of the vessel at their 

 death. Wintringham finds that the thickness 

 of the arterial coats is greater than that of 

 the aorta above the giving off of the renal ar- 

 teries, to which it bears the ratio of 1 to 0'762 ; 

 he also states that they will sustain a pres- 

 sure of 41 Ibs. 



The serous covering of the spleen receives 

 some unnamed small arteries : thus a twig is 

 given to it from the left inferior phrenic 

 artery, which courses in the phrenico-lienal 

 ligament ; and, besides this, it receives 

 branches from the first lumbar, from the left 

 spermatic, and from the splenic itself. Addi- 

 tionally to these, in some of the vertebrata, 

 to wit in the calf, small twigs in great number 

 leave the substance of the spleen, and after 

 perforating the fibrous coat of the organ 

 spread themselves out upon its surface. 



The splenic vein altogether corresponds in 

 distribution to the splenic artery. So many 

 primary arterial branches enter the hilus of 

 the spleen, and just as many veins come out 

 of it. These six to twelve veins unite into two 

 branches, and receiving, the upper the venoe 

 breves from the stomach, and the lower the 

 vena gastro-epiploica sinistra, they constitute 

 the trunk of the vein. In the spleen, and at 

 their emergence from it, the veins lie anterior 

 to the arteries, but then they place themselves 

 posteriorly to them ; and it is behind the 

 arteries that they unite to form the common 

 trunk. This trunk receives a twig from the 

 pancreas, from the lymphatics of the spleen, 

 from the stomach, and, further, the vena coro- 

 naria ventriculi ; it then passes away over the 

 aorta to the under surface of the liver ; and, 

 finally, with the vena mesenterica superior it 

 constitutes the trunk of the vena portse. 



The splenic vein, like all the branches of 

 the vena portae, has no valves, and is the 

 largest branch which assists to form that 

 trunk. Its width is very considerable: ac- 

 cording to E.Home* and Giesker, the propor- 

 tion to that of the arteries is as 5 to 1 ; and 

 according to earlier authorities it is yet more. 

 The proportionate size of the branches is still 

 larger ; and, according to C. A. Schmidt, their 

 ratio in the spleen itself to that of the arteries 



* On the Structure and Uses of the Spleen, Phil. 

 Trans, for 1808. 



which run with them is as 20 to 1. In con- 

 trast to this, the thickness of their coats is 

 very inconsiderable, and, according to Win- 

 tringham, is to that of the arteries as 1 to 

 4'8 or 4'3, to that of the iliac vein as 1 

 to 3-5. 



On their entry into the spleen, both arterial 

 and venous branches receive as a covering a 

 process of that "tunica propria" of the spleen 

 which forms the vagints vasorum, previously 

 described. 



These are not alike in all animals : thus, 

 for instance, they differ in man from those ex- 

 hibited by the higher brute mammalia a fact 

 which explains the various descriptions given 

 by different authors. In man, the sheaths of 

 the vessels form complete coats around them. 

 A section made in the centre of the hilus, and 

 continued through the spleen, exhibits them 

 very distinctly as projections or processes of 

 the tunica propria, and also allows their 

 further circumstances to be seen. It is thus 

 shown that arteries, veins, and nerves are 

 thickly enclosed in these sheaths ; but in 

 such wise that they are easily separated and 

 isolated, especially in old, or macerated, or 

 boiled spleens. The arteries and nerves 

 allow of this more easily than the veins, 

 which latter have a closer connection to these 

 sheaths. It is further seen that not only are 

 the trunks of entering and emerging vessels 

 thus covered, but that their finer ramifications 

 receive a similar clothing. The thickness of 

 these sheaths is in the human subject by no 

 means inconsiderable. As Giesker correctly 

 states, they are at first exactly the thickness 

 of the tunica propria, and retain the same 

 thickness for a considerable distance, that is, 

 as long as they clothe the main trunks of the 

 vessels. On the branches which proceed 

 laterally from these trunks, and on their fur- 

 ther extent, the sheaths become naturally 

 finer, and gradually increase this fineness as 

 the vessels become more minute, until finally, 

 becoming very delicate, they lose themselves 

 in the pulp of the spleen in the manner 

 previously mentioned. The thickness of a 

 sheath is always less than that of the coat of 

 the artery which it incloses, and greater than 

 that of the vein ; yet this does not hold good 

 of vessels in all parts of their extent, since on 

 the finest branches the sheaths are pro- 

 portionally somewhat stronger than on the 

 larger ones. As to the relations of the 

 sheaths to the rest of the spleen substance, 

 it must especially be considered that they do 

 not lie free in the parenchyma of the organ, 

 but are connected with the general trabecular 

 network by means of balks which are given 

 off from them: but these balks are not so 

 numerous as different anatomists appear to 

 think ; so that we are scarcely entitled to con- 

 sider with Giesker, that the whole trabecular 

 network is formed out of this connection. 



In other Mammalia, as in the horse, ass, 

 ox, pig, sheep, &c., the course of these sheaths 

 differs in some respects from that seen in 

 man. In the three latter animals, which in 

 this respect are best known to me, no 



