THE CIRCULATORY SYSTEM 



281 



The lymph spaces of the body stand in communication so 

 that there is a flow of lymph from the one to the other, but 

 of the course of the flow, if there be a constant one, little is 

 known. There is a flow of lymph into the blood through 

 the four lymph hearts and also through the ciliated nephro- 

 stomes on the ventral surface of the kidney which lead from 



Fig. 78. — Lymph sacs of Rana. The dark lines indicate where the septa 

 extend between the skin and the body. a, abdominal lymph sac ; b, 

 lateral brachial lymph sac; c, crural lymph sac ; d, dorsal lymph sac; 

 f, femoral lymph sac ; /, lateral lymph sac ; p, pectoral lymph sac; 

 s, submaxillary lymph sac. (Modified from Gaupp.) 



the coelom into the renal veins. The anterior lymph hearts 

 are situated just behind the transverse processes of the third 

 vertebra, and empty into the vertebral vein, which flows into 

 the internal jugular. The posterior lymph hearts lie on 

 either side of the tip of the urostyle, and empty into the 

 transverse iliac vein. All of the lymph hearts pulsate regu- 

 larly, antl pump the lymph from the lymph spaces with which 

 they communicate into the blood. At their openings into 

 the veins there is a pair of semilunar valves which prevent 

 the blood from passing into the lymph heart when it becomes 

 relaxed. At the opposite end there are ostia (but appar- 

 ently no valves) through which the lymph enters the heart 



