SPLEEN OF MAMMALIA. 



557 



429 



and hindrance to dilatation, prevent any local congestion of blood 

 pressing upon the brain. 



§ 350. Spleen of Mammalia. — As with the absorbents, so with 

 the bloodvessels, some change 

 their tubular for a lacunar or 

 cellular form in certain parts, 

 where the blood undergoes, or 

 receives elements of, change ; 

 such parts, resembling ( glands,' 

 are so called, with the qualifying 

 epithets of e vascular' or ' duct- 

 less.' Of these ( vasoganglions ' 

 the chief is the spleen. 



In Mammals this organ is 

 relatively larger than in lower 

 Vertebrates : it is mainly ap- 

 pended to the artery that sup- 

 plies the pancreas, with the left 

 end of which gland it is in 

 close connection, and conse- 

 quently lies to the left or be- 

 hind the stomach, to which it is 

 attached by the fold of perito- 

 neum noted at p. 500. This 

 membrane covers the whole spleen, except the ' hilus,' where its 

 two folds support the splenic vessels and form the 

 ' gastro-splenic' ligament. The serous tunic is less 

 intimately adherent to the fibrous or proper capsule 

 in most lower Mammals (Ruminants, e.g.) than in 

 Man ; where the separation only takes place at the 

 hilus. The proper coat consists mainly, and in Man 

 wholly, of white and yellow fibres, the former ar- 

 ranged in bands, the latter in an irregular network. 

 With these are blended, in some lower Mammals 

 (Dog, Pig, e.g.), filamentary fusiform bodies with 

 a nucleus, fig. 430, «, called" ( fibre-cells of un- 

 striped muscle' in ccvm". The fibrous tunic is 

 reflected into the interior at the hilus, in the form 

 of sheaths accompanying the vessels, most complete 

 in the human spleen: from the exterior of which 

 sheaths, and more abundantly from the inner sur- 

 face of the proper capsule, are sent off white elastic 

 6 trabecular ' bands, which form a reticular bed for 



Venous sinuses of dura mater, from behind, Human. 



430 



Nucleate filament or 

 * muscle-cell,' from 

 tunica propria of 

 the spleen of a 

 dog : magnified 350 

 diam. ccvm". 



