Florence E. Sabin 



361 



. and ear, by which the capiHaries over the face and the long plexus in the 

 neck were filled. 



In Fig'. G the lymph heart is still plain, showing as a triangle in the 

 depth. It has modified somewhat in shape, inasmuch as lymph nodes 

 are forming at the apex and base, making the angles of the triangle 

 appear as knobs. The apex of the sac is now labeled primary lymph 

 node, and the base is lettered h. The actual size of the triangle as a 

 whole is not greater than when the embryo was 3.6 cm. long. That is to 

 say, the distance from the apex to the base is about 4 mm. in either case. 



The ducts over the shoulder from the apex of the sac are well injected, 

 these being the first set to develop. The set of ducts which grows for- 

 ward from the apex of the sac over the surface of the sterno-cleido- 

 mastoid muscle to make the long plexus in the neck shows somewhat, but 

 is not as well injected in this specimen as 

 in Fig. 7. They are present at this 

 stage but the injection from the region 

 near the eye was not pushed quite far 

 enough to bring them out well. This set 

 of ducts develops into the long and abund- 

 ant plexus which follows the course of the 

 external jugular vein as it lies parallel to 

 the sterno-cleido-mastoid muscle. From 

 this long plexus, the entire face, front of 

 the neck, fore leg, and thorax are supplied 

 with lymphatics, and these different sets 

 can be seen in Fig. 6. All of these sets 

 of ducts anastomose in the skin, as can be 

 seen in Fig. 5, Vol. Ill, p. 188. 



In brief, the ducts for the shoulder and back of the head grow directly 

 from the lymph heart; those for the face, neck, and fore leg grow from 

 the lymph sac, but form a long plexus along tlie external jugular vein 

 before reaching the skin. As has just been said, both sets of ducts, dis- 

 tinct in the depth, anastomose in the surface. The line of growth of 

 the lymphatics has been tested by a large number of injections in every 

 stage from the time tlie lymphatics first appear up to the time of birth. 

 Every injection made into the ducts of the skin of the anterior part of 

 the body will run to the lymph sac or the gland derived from it, if pushed 

 far enough. The different systems of ducts of the neck can be brought 

 out by injecting in four different places. When the needle is entered 

 over the shoulder the injection mass invariably runs to the apex of the 

 28 



Fio. 4. Diagrara of the anterior 

 lymph heart in an embryo \ng, 3.6 

 cm. long. X 10. A, apex of the 

 heart ; h, base of the heart and level 

 of Fig. 5; ijv, internal jugular vein. 



