482 LYMPHATICS. 



The lymphatics are supplied by nutrient vessels, which are distributed to 

 their outer and middle coats ; but no nerves have at present been traced into 

 them. 



The lymphatics are very generally provided with valves, which assist materially 

 in effecting the circulation of the fluid they contain. They are formed of a thin 

 layer of fibrous tissue, lined on both surfaces with scaly epithelium. Their form 

 is semilunar ; they are attached by their convex edge to the sides of the vessel, 

 the concave edge being free, and directed in the course of the contained current. 

 Usually, two such valves, of equal size, are found placed opposite one another ; 

 but occasionally exceptions occur, especially at or near the anastomoses of lymphatic 

 vessels. Thus one valve may be of very rudimentary size, the other increased in 

 proportion. In other cases, the semilunar flaps have been found directed trans- 

 versely across the vessel, instead of obliquely, so as to impede the circulation in 

 both directions, but not to completely arrest it in either ; or the semilunar flaps, 

 taking the same direction, have been united on one side, so that they formed, by 

 their union, a transverse septum, having a partial transverse slit ; and sometimes 

 the flap was constituted of a circular fold, attached to the entire circumference of 

 the vessel, and having in its centre a circular or elliptical aperture, the arrange- 

 ments of the flaps being similar to those composing the ileo-csecal valve. 



The valves in the lymphatic vessels are placed at much shorter intervals than 

 in the veins. They are most numerous near the lymphatic glands, and they are 

 found more frequently in the lymphatics of the neck and upper extremity, than in 

 the lower. The wall of the lymphatics, 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 which they present. 

 Yalves are wanting in the vessels composing the plexiform network in which the 

 lymphatics originate. 



There is no satisfactory evidence to prove that any natural communication exists 

 between the lymphatics of glandular organs and their ducts, or between the 

 lymphatics and the capillary vessels. 



The lymphatic or absorbent glands, named also conglobate glands, are small 

 solid glandular bodies, situated in the course of the lymphatic and lacteal vessels. 

 They are found in the neck and on the external parts of the head ; in the upper 

 extremity, in the axilla and front of the elbow ; in the lower extremity, in the 

 groin and popliteal space. In the abdomen, they are found in large numbers in 

 the mesentery, and along the side of the aorta, vena cava, and iliac vessels ; and in 

 the thorax, in the anterior and posterior mediastina. They are somewhat flattened, 

 and of a round or oval form. In size, they vary from a hempseed to an almond, 

 and their color, on section, is of a pinkish-gray tint, excepting the bronchial 

 glands which in the adult are mottled with black. Each gland has a layer of 

 cellular tissue investing it, forming a capsule, from which prolongations dip into 

 its substance forming partitions. The lymphatic and lacteal vessels pass through 

 these bodies in their passage to the thoracic and lymphatic ducts. A lymphatic 

 or lacteal, previous to its entering a gland, divides into several small branches, which 

 are named afferent vessels. As they enter, their external coat becomes continuous 

 with the capsule of the gland, and the vessels, much thinned, and consisting only 

 of their internal coat and epithelium, pass into the gland, where, subdividing, 

 they pursue a tortuous course ; and finally anastomosing form a plexus. The 

 vessels composing this plexus unite to form two or more efferent vessels, which 

 on emerging from the gland are again invested with their external coat. Within 

 the lymphatic vessels, as supposed by Kolliker, Goodsir, and others, or lying 

 between them, grouped in cells, like the acini of secreting glands, is a large 

 number of minute dotted corpuscles. They are spheroidal or disk-shaped pellucid 

 particles, about -g^Vtr of an inch in diameter, having two or three minute dark 

 particles in their interior. It is probable that they play an important part in the 

 more complete elaboration of the lymph or chyle traversing the glands. Capillary 

 vessels are abundantly distributed on the walls of the lymphatics in the glands. 



