1448 



THE DUCTLESS GLANDS 



reticulura. The erythrocytes are on their way to or from the blood current ; the erythroblasts 

 are newly formed red blood cells that have as yet not lost their nuclei. The disintegrating 

 red cells are useless cells that by their disintegration contribute the coloring matters to the bile. 

 The branched cells are large, flattened, stellate elements, the processes of which seem to anas- 

 tomose to assist in forming the reticular substance, and also seem to connect with the endo- 

 thelial cells of the capillaries. The splenic cells are large polynuclear elements possessing 

 the power of ameboid movements. They often contain pigment granules and red cells in theii 

 protoplasm, thus indicating phagocytosis. The trabeculse are continuations of the capsule, 

 and consist of white fibrous connective tissue and smooth muscle tissue. 



The splenic (Malpighian) corpuscles are dense, spherical or cylindrical collections of lym- 

 phoid tissue (solitary follicles) surrounding an arteriole. Each corpuscle shows a lighter germinal 

 centre and a darker peripheral zone where the leukocytes are more numerous and more closely 

 packed. Each corpuscle usually exhibits an excentrically placed arteriole, as the lymphoid 

 tissue is collected in the adventitial sheath of the vessel. These bodies are visible to the naked 

 eye, and appear as whitish dots. 



Bloodvessels of the Spleen. 1 The splenic artery enters the hilum and divides into branches 

 that follow the trabeculse. Of these, some quickly pass to the pulp, while others follow the 

 trabeculae to their smallest divisions. The spleen is divided into circulatory lobules about 1 mm, 

 in diameter, each of which is divided into histological units, one for each terminal vessel, or 

 ampulla. These terminal vessels are large endothelial channels surrounded by a lymphatic 

 sheath, called the ellipsoidal sheath. These terminal ampullae are porous and continue as 

 veins, that collect the blood and empty it into the splenic vein at the hilum. 



Supporting cell. 



Vessel undergoing lymphoid change. 



Small 

 artery.' 



Vessel continuous 

 with processes of 

 supporting cells. 



cell. 



> '=V 



FIG. 1205. Section of spleen, showing the termination of the small bloodvessels. 



The spleen is subject to rhythmical contractions, one per minute; during a contraction the 

 organ is reduced about 18 per cent, in volume. These contractions are produced by the con- 

 tractions of the smooth muscle tissue in the capsule and trabeculae of the pulp. 'When the 

 cardiac impulse sends the blood into the arterial channels the blood passes through the porous 

 walls of the ampullae into the pulp. When the rhythmical contractions occur the blood is forced 

 into the veins through the pores of the ampullae, and at the same time the arteries are closed. 



The lymphatics originate in two ways i. e. from the sheath of the arteries and in the 

 trabeculae. The former trunks are the deep collecting trunks, and accompany the blood- 

 vessels; the latter pass to the superficial lymphatic plexus, which may be seen oil the surface 

 of the organ. Lymphatic channels do not exist in the pulp. The deep trunks at the hilurn 

 number from five to ten, and terminate in the splenic nodes. The superficial trunks also pass 

 to the hilum and terminate in the splenic nodes. . 



The nerves are derived from the splenic plexus, which is a part of or connected with the 

 solar plexus. The nerves enter the spleen with the vessels. 



Surface Form. The spleen is situated under cover of the lower ribs of the left side, being 

 separated from them by the Diaphragm, and above by a small portion of the lower margin of 

 the left lung and pleura. Its position corresponds to the ninth, tenth, and eleventh ribs. It is 

 placed very obliquely. " It is oblique in two directions viz., from above downward and outward, 

 and also from above downward and forward" (Cunningham). "Its highest and lowest points 

 are on a level respectively with the ninth thoracic and first lumbar spines; its inner end is dis- 



1 F. P. Mall, Amer. Jour, of Anat., 1903, vol. ii, No. 3. 



