752 



ORGANS OF DIGESTION. 



great end of the stomach, and at the upper end of the organ on to the Dia- 

 phragm. 



The fibrous elastic coat forms the framework of the spleen. It invests the 

 exterior of the organ, and the hilum is reflected inwards upon the vessels in 

 the form of vaginae or sheaths. From these sheaths, as well as from the inner 

 surface of the fibro-elastic coat, numerous small fibrous bands, trdbeculse (Fig. 

 414), are given off in all directions ; these uniting, constitute the areolar frame- 

 work of the spleen. The proper coat, the sheaths of the vessels, and the trabe- 

 culae, consist of a dense mesh of white and yellow elastic fibrous tissues, the 

 latter considerably predominating. It is owing to the presence of this tissue, 

 that the spleen possesses a considerable amount of elasticity, to allow of the 

 very considerable variations in size that it presents under certain circumstances. 

 In some of the mammalia, in addition to the usual constituents of this tunic, 

 there are found numerous pale, flattened, spindle-shaped, nucleated fibres, like 

 unstriped muscular fibres. It is probably owing to this structure that the spleen 

 possesses, when acted upon by the galvanic current, faint traces of contractility. 



The proper substance of the spleen occupies the interspaces of the areolar 

 framework of the organ ; it is a soft, pulpy mass, of a dark reddish-brown color, 

 consisting of colorless and colored elements. 



The colorless elements consist of granular matter-; nuclei, about the size of the 

 red blood-disks, homogeneous or granular in structure ; and nucleated vesicles 



Fig. 415.- The Malpighian Corpuscles, and their Relation with the Splenic Artery and its 



Branches. 



in small numbers. These elements form, probably, one-half or two-thirds of 

 .the whole substance of the pulp, filling up the interspaces formed by the par- 

 titions of the spleen, and lying in close contact with the walls of the capillary 

 vessels, so as to be readily acted upon by the nutrient fluid which permeates 

 them. Thus in well-nourished animals, they form a large part of the entire bulk 

 of the spleen, whilst they diminish in number, and occasionally arc wanting in 

 starved animals. The application of chemical tests shows that they are essen- 

 tially a proteine compound. 



The colored elements of the pulp consist of red blood-globules and of colored 

 corpuscles, either free, or included in cells. Sometimes, unchanged blood-disks 



