50 ADMONT H. CLARK 



in figures 505 and 506 of the Handbuch der Entwickelungsge- 

 schichte des Menschen. Keibel and Mali., vol. 2, 1911, ps. 708-709, 

 after Sabin. The third group of vessels is from the anterior cur- 

 vature of the sac where it arches dorsalward and lateralward 

 behind the pharynx. The importance of these vessels is shown 

 both by their size and their early appearance. In an embryo 2.8 

 cm. long the anterior curvature has a distinct bulge protruding 

 toward the buccal cavity, and in one specimen a few ducts can be 

 seen radiating toward the pharynx. From this retropharyn- 

 geal process of the sac are to be developed all of the lymphatics 

 of the pharynx, Eustachian tube, the nasal cavity and a part of 

 those of the tongue. The fourth group of vessels is by far the 

 largest. In figure 2 will be seen a group of vessels from the ventral 

 border of the apex of the sac which grow ventralward external 

 to the sterno-cleido-mastoid muscle and form an extensive lym- 

 phatic plexus along the course of the external jugular vein. This 

 plexus I shall call the superficial cervical plexus since it gives 

 rise to the superficial cervical lymph glands. 



The injection shown in figure 2 is not a complete injection for 

 these vessels. The point of injection was in the suprascapular 

 vessels which is an indirect point for the superficial cervical plexus. 

 The vessels from the ventral border of the apex of the sac are 

 present in an embryo 18 mm. long and hence they begin at about 

 the same time as the suprascapular lymphatics. The superficial 

 cervical plexus as shown in figure 2 has already sent a group of 

 vessels cranialward, part of which are shown as posterior auricular 

 lymphatics. The vessels which grow forward along the external 

 jugular vein divide into two groups,- the temporal and the facial. 

 From the ventral border of the superficial cervical plexus develop 



Fig. 2 Injection of the jugular lymph sac in an embryo pig measuring 3.5 cm. 

 long. Magnified about 10 times. This is the same specimen which was shown as 

 figure 3 in The American Journal of Anatomy, p. 186, vol. 3, 1904. The specimen 

 has since been cleared by the Spalteholz method so that it shows the relation of 

 the superficial lymphatics to the jugular lymph sac. It is a complete injection of 

 the suprascapular and occipital plexuses and an incomplete injection of the begin- 

 ing cervical plexus. The sac stalk shows faintly where it extends internal to the 

 arm. F.v, faciiil vein; a little blood in this vein enables one to locate the position 

 of the superficial cervical lymphatic plexus. 



