56 ADMONT H. CLAKK 



the sac which follow the external jugular vein. This group of 

 \'('ss(4s is indicated by one trunk in figure 1, but the vessels show 

 much better in a mesial view. Mesial sections of pigs 5 to 6 cm. 

 long show that there is an abundant plexus of vessels arising 

 from the stalk of the sac in the root of the neck near the place 

 where the lymphatic sac connects with the vein. A few of these 

 vessels follow the stalk or deep jugular trunk and are mentioned 

 in connection w4th the lymphatics of the pharynx, more of them 

 however follow the external j ugular vein and connect with or help 

 to form the superficial cervical plexus. In one specimen, one of 

 these vessels connects directly with the external jugular vein 

 instead of with the sac stalk. Thus the superficial cervical plexus 

 can be said to arise not only from the apex of the sac but from the 

 sac stalk as well or even by a variation directly from the veins. 

 The plexus of vessels which follows the external jugular vein is 

 very conspicuous in injections of cat embryos where the vein is 

 entirely surrounded by a plexus of lymphatics. 



In the pig 5.5 cm. long the cranial end of the cervical plexus 

 gives rise to three sets of lymphatics. First there are vessels 

 growing behind the ear making a posterior auricular set. There is 

 also a secondary plexus of vessels close to the main plexus which 

 supplies (2) the temporal lymphatics and (3) the facial vessels. 

 From the ventral border of the cervical plexus grow a group of 

 deep submaxillary vessels and a very abundant plexus of vessels 

 for the skin of the neck. The submaxillary plexus supplies the 

 lower jaw and tongue and it has anastomoses both with the facial 

 group and with the vessels from the anterior curvature of the 

 sac. The submaxillary plexus may also connect with vessels 

 along the internal jugular vein. The importance of these anas- 

 tomoses between the primary groups of vessels cannot be empha- 

 sized too much. 



The caudal end of the cervical plexus extends directly into the 

 superficial thoracic vessels and supplies also the superficial lym- 

 phatics of the arm. These would show better in a ventral view 

 than they do in the lateral one. In this point the drainage in the 

 pig is different from that of the human embryo where the large 

 thoracic vessels and the superficial vessels of the shoulder drain 



