106 BLOOD-GLANDS AND DUCTLESS GLANDS. 



sage from artery to vein. Toward the terminations of the 

 bloodvessels, openings appear in their walls, and the vessels 

 become lost in the sinuses, the endothelium of the tunica 

 intima merging into the flat connective-tissue cells incom- 

 pletely lining the reticulum. 



The parenchyma of the spleen is mostly made up of the 

 splenic pulp. This consists of the open network of sinuses 

 filled with plasma and free cells, some of which are peculiar 

 to this situation, others derived from the blood-stream passing 

 through. The free elements of the pulp are : red blood-cor- 

 puscles in great abundance ; lymphoid cells and leukocytes of 

 all kinds ; large multi nucleated amoeboid granular cells ; and 

 pigment-granules, free or within the leukocytes and amoeboid 

 cells, derived from the disintegration of the hemoglobin of 

 broken-down red blood-corpuscles. 



The spleen is supplied with lymphatic vessels, which are 

 much less conspicuous than the blood-supply. 



Scattered about through the substance of the spleen are 

 numerous spherical or oval nodules or follicles of typical 

 lymphoid tissue, the Malpighian corpuscles. These occur sur- 

 rounding small-sized arteries, which pierce them at or near 

 their centres. 



The function of the spleen is not thoroughly understood ; 

 it is concerned with the formation or purification of the blood. 

 It may be a seat for the removal of worn-out red blood-cor- 

 puscles. Whether it contributes any corpuscular elements to 

 the blood has not been settled. 



The coccygeal gland (Luschka's gland) is a small, round 

 pea-sized body, near the tip of the coccyx, in which the 

 middle sacral artery terminates. It consists of a plexus of 

 dilated capillaries, or even cavernous blood-sinuses, which 

 are surrounded by masses of granular polyhedral connective- 

 tissue cells. The gland is enveloped by a fibrous capsule, 

 from which trabeculaB pass into the interior. It is plentifully 

 supplied with nerves. Its function is unknown. 



The carotid glands are small bodies situated in the bifurca- 

 tion of the common carotid arteries, one on each side. Their 

 structure is similar to that of the coccygeal gland. 



