THE DEVELOPMENT OF THE VASCULAR SYSTEM. 



245 



(2) The peripheral lymph channels, which drain into the thoracic duct, 

 represent outgrowths from the lymph sacs. From the jugular sacs sprouts 



oj 



' 



FIG. 215. From cross-sections of cat embryos in successive stages (<z, b, c, d) of development, 

 in the region of the jugular lymph sac; diagrammatic but amply supported by studies of serial 

 sections and reconstructions. Huntington. 



i, Anterior cardinal vein; 2, somatic tributary of same; 4, developing blood cells in the mesen- 

 chyme; 5, mesenchymal intercellular spaces rudiments of the jugular lymph sac; 6, rudi- 

 merits of brachio-cephalic venous anastomosis; 7, brachio-cephalic venous anastomosis; 8, 

 haemophoric lymphatic plexus forerunner of jugular lymph sac; u, thoracic duct- 

 'approach' of jugular lymph sac; 12, rudiments of thoracic duct; 13, jugular lymph sac pre- 

 paring to rejoin vein and to establish secondary connection with rudiments of thoracic 

 duct (12) and of other systemic lymphatics (14); 15, jugular lymph sac, which has re- 

 joined vein through permanent lymphatico-venous tap (16); 17, thoracic duct; 1 8, jugular 

 and cephalic systemic lymphatics. 



invade the neck, head, shoulders, and finally the entire upper extremities 

 and upper part of the body wall (Fig. 214). Similarly, from the posterior 

 lymph hearts sprouts invade the lower extremities and lower portion of the 



