JUGULAR LYMPH SACS AND CHANNELS NECK OF PIG 53 



lymphatic plexus is a complete layer of lymphatics covering the 

 body. This stage is shown in Sabin's figure 5 in The American 

 Journal of Anatomy, p. 188, volume 3, 1904 In this figure it is 

 not possible to analyze the primary plexuses; the suprascapular, 

 occipital, posterior auricular, temporal, facial, cervical, thoracic 

 and brachial vessels make one continuous plexus. When an 

 injected specimen of this stage is cleared however by the Spalte- 

 holz method the place of origin for each plexus can be made out. 

 In figure 3 it is clear that the primary lymph sac has the three 

 divisions already given, namely, the apex in the posterior triangle 

 the anterior curvature and the sac stalk lying deeper and hence 

 showing very faintly on the internal jugular vein. The apex of the 

 sac and the anterior curvature may now be called lymph glands, 

 the sac stalk however remains as the deep jugular lymph trunks. 

 In comparing figures 2 and 3 it is clear that in the earlier stage the 

 outline of the sac is a comparatively smooth curve from the stalk 

 around to the apex. In an embryo pig 20 mm. long the entire 

 dorsal border of the sac has a series of sprouts but the permanent 

 ducts are however limited to certain areas along the sac and these 

 parts enlarge while the intermediate parts remain small. This 

 determines the position of the lymph nodes. 



Three factors seem to guide this primary node formation in the 

 sac. First the apex of the sac receiving as it does the suprascapu- 

 lar and occipital vessels directly and all of the vessels of the face, 

 neck, arm and thorax indirectly through the superficial cervical 

 plexus is the largest center of drainage in the neck. Lymph 

 glands develop at the centers of drainage and the apex of the sac 

 therefore becomes an early and a large node. Second the portion 

 of the sac between the apex and the anterior curvature can be 

 assumed to be comparatively non-functional as a path for lymph 

 conduction, for the apical drainage would most easily pass to the 

 veins by way of the cross connection to the stalk. Hence the por- 

 tion of the sac intervening between the apex and the anterior 

 curvature remains small. Third, the development of the sterno- 

 cleido-mastoid muscle which crosses the sac between the apex and 

 the anterior curvature probably causes a pressure to be exerted 

 at this point. Drainage, function and structural relations can 



