354 THE SPLEEN, BY WILHELM MU LLER. 



trabeculsB must, moreover, exert pressure upon the intervening 

 parenchyma which compels the movement of such of the con- 

 stituents of the latter as are capable of changing their position 

 to those parts where the tension is least (W. Miiller). 



ARTERIAL SHEATHS. At their entrance into the hilus of the 

 organ the arteries receive a sheath from the capsule with which 

 the proper vascular wall is loosely connected. This sheath con- 

 sists of fibrillar connective tissue with numerous elastic fibres, 

 and a moderate proportion of cell elements lying between the fas- 

 ciculi, the latter appearing partly as rounded lymph corpuscle- 

 like bodies, and partly as elliptical nuclei which only present small 

 masses of protoplasm at their poles. The sheaths accompany 

 the arterial branches, without essential modification in their 

 structure, to the points at which the arteries and veins previ- 

 ously running together separate from one another, which usually 

 occurs in the arterial branches, of from O3 to 0'2 millimeter in 

 diameter. From this point onwards the arterial sheaths pre- 

 sent a remarkable modification in their structure, which consists 

 in the conversion of their connective tissue into a cytogenous 

 tissue, whilst at the same time it becomes much looser in tex- 

 ture. The connective tissue bundles throughout the whole 

 thickness of the sheath become coincidentally much looser ; 

 their fibrils become more delicate, and lymph corpuscle-like 

 cells are abundantly found in their interstices. A cylindrical 

 sheath, rich in cells, is thus formed, which accompanies the 

 arterial branches either to their entrance into the blood pas- 

 sages of the pulp, as in Fishes, Amphibia and Chelonia, or to 

 their passage into the capillaries, as in Birds and Mammals. In 

 the first-named animals it is only seldom that any further 

 development of these sheaths occurs ; in Birds and Mammals, 

 on the other hand, rounded or ellipsoidal sharply circumscribed 

 bodies, varying from O3 to 1 millimeter in diameter, appear with 

 great regularity, termed the Malpighian bodies of the spleen, 

 which are easily recognisable with the naked eye, on account of 

 their whitish colour. They represent, as is now generally ad- 

 mitted, local hyperplasise of the cytogenous connective tissue 

 of the arterial sheaths. Their disposition upon the arterial 

 branches to which they belong varies to some extent, according 



