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CHAPTER XXXV. 



ON THE DUCTLESS GLANDS. SPLEEN. ITS CAPSULE. TRABECULAR 



TISSUE. SPLEEN PULP. SPLENIC ARTERY. MALPIGHIAN CORPUS- 

 CLES. VEINS OF THE SPLEEN. LYMPHATICS. NERVES. 



CHANGES IN THE BLOOD IN THE SPLEEN. USES OF THE SPLEEN. 



SUPRA-RENAL CAPSULES. THYROID BODY. USES OF THE 



THYROID. THYMUS. USES OF THE THYMUS. , 



WE have now to consider a remarkable class of organs present 

 in all the mammalia, which resemble the secretory glands already 

 described in external conformation and in the possession of a solid 

 parenchyma, but differ from them in the absence of any excretory 

 apparatus suitable for carrying off the products of secretion. These 

 organs cannot be associated with such structures as the liver, the 

 kidneys, and the other glands ; inasmuch as they not only differ 

 from them in the essential particular just mentioned; but they 

 exhibit in their internal structure no mechanical arrangement 

 clearly adapted to a secretory function ; nor is any material (save 

 in the case of the thymus) to be obtained from them bearing any 

 resemblance to a secreted product. Many physiologists, however, 

 suppose that these organs do exert an attractive influence on cer- 

 tain matters in the blood, and separate them from it; but this 

 hypothesis necessarily involves a second and a less plausible one, 

 that the matter thus extracted must re-enter the circulation. 



These bodies agree in the common characteristic, that their pa- 

 renchymatous portion consists of cells and cell-nuclei, with blood- 

 vessels in great number variously disposed. They may probably 

 be regarded as appendages to the vascular system, and, from the 

 absence of any excretory duct, they are usually designated vascular 

 ductless glands : under this head are grouped the spleen, the 

 supra-renal capsules, the thyroid body, and the thymus. 



Spleen. The spleen is of an oval form and somewhat compressed ; 





