SECT. 169.] VESSELS OF THE SPLEEN. 367 



the spleen, and there appears no constant relation between them and the 

 state of digestion. In the third place, we must remember that very similar 

 phenomena are observed with some constancy in other places, where they are 

 never supposed to be physiological, as in little effusions of blood in the 

 lungs, bronchial glands and thyroid of man, and in the mesenteric glands of 

 the pig and rabbit. 



From these considerations, I was forced (as early as 1854) to abandon the 

 view, that the changes of the blood-discs in the splenic pulp belonged to the 

 series of physiological appearances ; I conceived that such changes, to be 

 normal, must occur in the interior of vessels, and in this opinion I find 

 myself supported by the great majority of physiologists. I am still of opinion 

 that a solution of blood-cells actually does go on within the spleen, and in 

 this organ much more than in the liver. But I have conclusively given up 

 the grounds on which I originally upheld the physiological nature of this 

 change, for I can no longer regard the occurrence of decomposed blood-cells 

 in the pulp as establishing such a view. 



§ 169. Vessels and Nerves. — At tlieir entrance into the spleen, 

 the splenic artery is relatively very large, and, with the still larger 

 vein, is immediately surrounded by the continuations of the fibrous 

 coat, the sheaths of the vessels. In man, these sheaths completely 

 invest the vessels and nerves, somewhat after the manner of the 

 capsule of Glisson. The arteries and nerves may be very readily 

 isolated, the veins are more firmly connected with this sheath near 

 the hilus. Around the main branches of the vessels the thickness 

 of the sheaths is the same as that of their fibrous coats ; but the finer 

 branches of the vessels have thinner and thinner envelopes, until, 

 on the most delicate vessels, the sheaths become very fine mem- 

 branes, and lose themselves in the pulp. The thickness of a sheath 

 is always less than the wall of the vein to which it belongs. As 

 has been above mentioned, a number of trabecular become attached 

 to the sheaths of the vessels, and the trabecular, sheaths, and 

 vessels together take part in the formation of the dense network 

 in the interior of the organ. — In mammalian animals, as in the 

 horse, ass, ox, pig, sheep, etc., the sheaths present a different ar- 

 rangement, being absent altogether from the smaller veins, and 

 being met with, on the larger ones, only upon the side nearest to 

 the arteries and nerves. It is only the two main venous trunks at 

 the hilus which possess complete sheaths, whilst, on the arteries, a 

 perfect investment may be traced, even to their finest ramifications. 

 The structure of the sheaths is quite that of the trabecular, except 

 that where the latter contain muscular fibres, such fibres are not 

 always found in the former. Thus they are absent in the sheaths 

 of the ox-spleen, though perfectly distinct in those of the pig. 



