ANATOMY OF SEROUS MEMBRANES. 143 



only to the serous membranes, to which we have for the 

 present confined our attention ; the experimental researches 

 we must leave unnoticed in this place. 



^ Our investigations relate to more than 250 animals, espe- 

 cially rabbits and guinea pigs, many frogs, several cats, 

 dogs, some rats, and one monkey. 



I. The centrum tendineum of the diaphragm. 



(a) Under normal conditions. The lymphatic vessels of the 

 centrum tendineum are in each half arranged in two systems, 

 an anterior and posterior. 



The vessels of the anterior system are distributed upon 

 the outer and anterior (that is, larger) division of the ante- 

 rior quadrant, and upon the outer (that is, smaller) division 

 of the anterior quadrant. Those of the posterior system 

 are distributed upon the inner posterior (that is, smaller) 

 division of the anterior quadrant, and upon the inner (that 

 is, larger) division of the posterior quadrant. 



The efferent trunks of the anterior system course along 

 the Pars costalis of the diaphragm, and unite on the posterior 

 surface of the xiphoid cartilage on each side usually to a 

 single large vessel which runs along with the mammary 

 vessels and enters the sternal gland. The efferent trunk of 

 the posterior system is single on each side : it mounts ob- 

 liquely towards the middle line and opens into the thoracic 

 duct near the point Avhere the latter emerges from the dia- 

 ghragm. The larger lymphatic vessels of each system run 

 between the serous covering of the pleural side and the pars 

 tendinea. The lymph-capillaries which arise from them and 

 are united together are as follows : — First, winding vessels 

 of various length which are situated between the Pleura and 

 the pars tendinea. Secondly, those which lie partly between 

 the serosa and the pars tendinea, and partly in the latter ; 

 and, finally, those which belong wholly to the pars tendinea. 

 Those of the first and second groups show dilatations or 

 sinuses ; those of the third group have an extended course 

 and lie imbedded between the tendinous bundles. In the 

 rabbit and the guinea pig there are two such layers of longi- 

 tudinally extended capillaries corresponding to the two sets 

 of lymphatic fissures described by Ludwig and Schweigger- 

 Seidel, the deep set which are between the circular bundles, 

 and the superficial which are between the radiating bundles 

 of the tendon. 



The longitudinally extended capillaries which we will call 



