304 HAND-BOOK OF PHYSIOLOGY. 



tity to distend them, the injected substance may be almost directly 

 afterward found in the lymphatics. 



Some other matters than those originally contained in the exuded 

 liquor sanguinis may, however, find their way with it into the lymphatic 

 vessels. Parts which having entered into the composition of a tissue, 

 and, having fulfilled their purpose, require to be removed, may not be 

 altogether excrementitious, but may admit of being reorganized and 

 adapted again for nutrition; and these may be absorbed by the lym- 

 phatics, and elaborated with the other contents of the lymph in passing 

 through the glands. 



Lymph-Hearts. In reptiles and some birds, an important auxiliary 

 to the movement of the lymph and chyle is supplied in certain muscular 

 sacs, named lymph-hearts (Fig. 217), and it has been shown that the 

 caudal heart of the eel is a lymph-heart also. The number and position 

 of these organs vary. In frogs and toads there are usually four, two 

 anterior and two posterior; in the frog, the posterior lymph-heart on each 

 side is situated in the ischiatic region, just beneath the skin; the anterior 

 lies deeper, just over the transverse process of the third vertebra. Into 

 each of these cavities several lymphatics open, the orifices of the vessels 

 being guarded by valves, which prevent the retrograde passage of the 



FIG. 217. Lymphatic heart ( 9 lines long, 4 lines broad) of a large species of serpent, the Python, 

 bivittatus. 4. The external cellular coat. 5. The thick muscular coat. Four muscular columns run 

 across its cavity, which communicates with three lymphatics (1 only one is seen here), and with two- 

 veins (2, 2). 6. The smooth lining membrane of the cavity. 7. A small appendage, or auricle, the cav- 

 ity of which is continuous with that of the rest of the organ (after E. Weber). 



lymph. From each heart a single vein proceeds and conveys the lymph 

 directly into the venous system. In the frog, the inferior lymphatic 

 heart, on each side, pours its lymph into a branch of the ischiatic vein; 

 by the superior, the lymph is forced into a branch of the jugular vein, 

 which issues from its anterior surface, and which becomes turgid each 

 time that the sac contracts. Blood is prevented from passing from the 

 vein into the lymphatic heart by a valve at its orifice. 



The muscular coat of these hearts is of variable thickness; in some 

 cases it can only be discovered by means of the microscope; but in every 

 case it is composed of striped fibres. The contractions of the heart are 

 rhythmical, occurring about sixty times in a minute, slowly, and, in com- 

 parison with those of the blood-hearts, feebly. The pulsations of the 



