364 



Development of the Lympliatic Nodes in the Pig 



passed through ducts that lie over the sterno-chleido-mastoid muscle into 

 the node representing the l3anph heart (pin). At this stage there are 

 two lymph nodes at the angle of the jaw, nf, one deeper, receiving the 

 ducts around the eye and cheek, the other more superficial, receiving 

 the ducts just in front of the ear. The rest of the long plexus is also 

 being modified into lymph nodes, one of which is in the middle of the 

 plexus where the ducts join with the lymph sac, the other is at the 

 posterior end of the plexus and drains the fore leg (nfl). 



Fig. 7. Lymphatics in the neck of an embryo pig, 11 cm. long, x 1%. 

 Lp, lymph plexus which lies parallel to the external jugular vein; nf, nodes 

 developing in the long plexus draining the face; nfl, node developing in the 

 long plexus and draining the fore leg; pin, primary lymph node between the 

 trapezius and sterno-cleido-mastoid muscles. 



Since the spread of the superficial lymphatic capillaries in the skin 

 of the pig is practically complete when the embryo is 6.5 cm, long, it 

 may be well to sum up the superficial lymphatic system at that stage. 

 In the neck there is, in the depth, the lymph heart now considerably 

 modified by the formation of lymph nodes. It has one large efferent 

 duct along the internal jugular vein and one along the main superficial 

 vein of the shoulder. Secondly, there is a plexus of ducts along the 

 external jugular vein; this plexus connects freely with the lymph heart. 

 Lymphatic nodes in the neck are to be found developing first from the 

 lymph sac, secondly in the long plexus on the course of the external jug- 



