58 ADAIUNT H. CLAKK 



rather than the roundabout course through the submaxillary 

 plexus. Thus it is clear that the deep lymphatics for the head and 

 neck come from the sac stalk and its extension the anterior cur- 

 vature. A part of them however, namely the submaxillary group 

 come from the cervical plexus. 



To sum up the relations of the superficial lymphatic vessels 

 to the jugular lymph sac; three groups of vessels arise from the 

 apex of the sac and therefore drain into the gland of the posterior 

 triangle of the neck, the suprascapular vessels, the occipital 

 vessels and the superficial cervical plexus. This latter extensive 

 plexus has a double origin coming from the sac stalk as well 

 or even by a variation directly from the vein. The stage of 5 to 

 6 mm. represents the time when all of the primary superficial 

 plexuses have been formed and have anastomosed with others in 

 the skin so that there may be said to be one continuous plexus of 

 lymphatic capillaries which covers the body. This plexus will 

 become the deep subcutaneous plexus of lymphatic ducts. The 

 development of valves in this plexus which now begins makes 

 it impossible to obtain such extensive injections as can be made 

 in embryos 5 to 6 cm. long but the development of the valves 

 tends again to bring out the primary plexuses which were lost by 

 the development of the anastomoses. 



From the anterior curvature of the sac and in part from the 

 stalk of the sac develop the vessels for the pharynx and nose. 

 These together with the submaxillary vessels from the cervical 

 plexus represent the deep lymphatics for the head and neck. 



All injections of later stages bring out the fact that the jugular 

 lymph sac develops into two lymph glands and the deep jugular 

 lymph trunk. In figure 4 is shown an injection of the deep lym- 

 phatics in the neck of a pig 7.5 cm. long. It shows particularly 

 well the position of the apex of the sac which is now a gland in 

 the posterior triangle of the neck, between the sterno-cleido-mas- 

 toid and the trapezius muscles. The anterior curvature of the 

 sac with some of the pharyngeal vessels lies under the sterno- 

 cleido-mastoid nmscle. It is also a lymph gland. The sac stalk 

 which is joined by the duct from the apex shows where it emerges 

 from beneath the muscle. On the surface of the sterno-cleido- 



