XIX] 



LYMPHATIC SYSTEM 



435 



trunks of the system open into the large veins. The finer branches 

 of the system ramify amongst all the organs of the body. There 

 is no circulatory current in the lymph canals except in those 

 belonging to the viscera, but 

 there are valves, arranged so 

 that when the lymph vessels 

 are squeezed by the increase 

 in diameter . of neighbouring 

 muscles when these contract, 

 fluid can pass forwards in one 

 direction but not backwards. 

 It will be seen that in 

 Craniata, unlike Arthropoda 

 and Mollusca, the blood, being 

 everywhere confined to vessels 

 with definite walls, does not 

 directly bathe the tissues of 

 any organ ; but that materials 

 must first diffuse through the 

 walls of the blood-vessels into 

 the lymph-spaces before they 

 can reach the tissue. One 

 explanation of the separation 



FIG. 214. Diagram of the venous 

 system of Mustelus antarcticus. 

 From T. J. Parker. 



1. Orbital sinus. 2. Hyoidean 

 vein. 3. Ductus Cuvieri. 



4. Anterior cardinal veiu. 5. 

 Jugular vein. 6. Conus arteri- 

 osus. 7. Ventricle. 8. Atrium. 

 9. Sinus venosus. 10. Hepatic 

 vein. 11. Liver. 12. Hepatic 

 vein. 13. Hepatic portal vein. 

 14. Left cardinal vein. 15. Bra- 

 chial vein. 16. Subclavian 



vein. 17. Gonad. 18. Pos- 

 terior cardinal vein. 19. Sper- 

 matic vein. 20. Lateral vein. 

 21. Eenal portaK veins from 

 caudal vein to kidney. 22. 

 Eight posterior cardinal vein. 

 23. Alimentary canal. 24. Vein 

 connecting orbital sinuses. 25. 

 Subintestinal vein. 26. Kidney. 

 27. Pelvic vein. 28. Cloacal 

 vein. 29. Femoral vein. 30. 

 Caudal vein. 



17 -Y\ t- 



30 



