STRUC 



The kidney is supplied with a coarse subserous plexus and a deeper plexus of 

 finer capillaries in the capsule. Lymphatics have been described within the sub- 

 stance of the kidney surrounding the tubules. 



The urinary bladder has a rich plexus of lymphatic capillaries just beneath the 

 epithelial lining, also a subserous set w r hich anastomoses with the former through 

 the muscle layer. The submucous plexus is continuous with the submucous plexus 

 of the urethra. 



The prostate has a rich lymphatic plexus surrounding the gland and a wide- 

 meshed subcapsular plexus. 



The testis has a rich superficial plexus beneath the tunica albuginea. The pres- 

 ence of deep lymphatics is disputed. 



The uterus is provided with a subserous plexus, the deeper lymphatics are 

 uncertain. Subepithelial plexuses are found in the vagina. 



The ovary has a rich superficial plexus and a deep interstitial plexus. 



The heart has a rich subserous plexus beneath the epicardium. Lymphatic 

 capillaries have also been described beneath the endocardium and throughout 

 the muscle. 



Lymphatic capillaries are probably absent in the central nervous system, the 

 meninges, the eyeball (except the conjunctiva), the orbit, the internal ear, within 

 striated muscle, the liver lobule, the spleen pulp and kidney parenchyma. They 

 are entirely absent in cartilage. In many places further investigation is needed. . 



Lymphatic Vessels. The lymphatic vessels are exceedingly delicate, and their 

 coats are so transparent that the fluid they contain is readily seen through them. 

 They are interrupted at intervals by constrictions, which give them a knotted 

 or beaded appearance; these constrictions correspond to the situations of valves 

 in their interior. Lymphatic vessels have been found in nearly every texture 

 and organ of the body which contains bloodvessels. Such non-vascular structures 

 as cartilage, the nails, cuticle, and hair have none, but with these exceptions it is 

 probable that eventually all parts will be found to be permeated by these vessels. 



Structure of Lymphatic Vessels. The larger lymphatic vessels are each composed of three 

 coats. The internal coat is thin, transparent, slightly elastic, and consists of a layer of elongated 

 endothelial cells with wavy margins by which the contiguous cells are dovetailed into one another; 

 the cells are supported on an elastic membrane. The middle coat is composed of smooth muscular 

 and fine elastic fibers, disposed in a transverse direction. The external coat consists of connective 

 tissue, intermixed with smooth muscular fibers longitudinally or obliquely disposed; it forms 

 a protective covering to the other coats, and serves to connect the vessel with the neighboring 

 structures. In the smaller vessels there are no muscular or elastic fibers, and the wall consists 

 only of a connective-tissue coat, lined by endothelium. The thoracic duct has a more complex 

 structure than the other lymphatic vessels; it presents a distinct subendothelial layer of branched 

 corpuscles, similar to that found in the arteries; in the middle coat there is, in addition to the 

 muscular and elastic fibers, a layer of connective tissue with its fibers arranged longitudinally. 

 The lymphatic vessels are supplied by nutrient vessels, which are distributed to their outer 

 and middle coats; and here also have been traced many non-medullated nerves in the form of 

 a fine plexus of fibrils. 



The valves of the lymphatic vessels are formed of thin layers of fibrous tissue covered on both 

 surfaces by endothelium which presents the same arrangement as on the valves of veins (p. 501). 

 In form the valves are semilunar; they are attached by their convex edges to the wall of the 

 vessel, the concave edges being free and directed along the course of the contained current. 

 Usually two such valves, of equal size, are found opposite one another; but occasionally excep- 

 tions occur, especially at or near the anastomoses of lymphatic vessels. Thus, one valve may 

 be of small size and the other increased in proportion. 



In the lymphatic vessels the valves are placed at much shorter intervals than in the veins. 

 They are most numerous near the lymph glands, and are found more frequently in the lymphatic 

 vessels of the neck and upper extremity than in those of the lower extremity. The wall of 

 the lymphatic vessel immediately above the point of attachment of each segment of a valve is 

 expanded into a pouch or sinus which gives to these vessels, when distended, the knotted or 

 beaded appearance already referred to. Valves are wanting in the vessels composing the plexi- 

 form net-work in which the lymphatic vessels usually originate on the surface of the body. 





