Florence E. Sabin 359 



ward with the apex, marked a in the diagram, near the surface, adjacent 

 to a superficial vein over the shoukler. This apex is to be found in the 

 triangle between the sterno-cleido-mastoid muscle and the trapezius. 

 From the apex of the sac, a duct follows along the vein of the shoulder 

 and empties into the duct along the internal jugular vein. This duct 

 becomes the main duct of the sac. 



Figure 3 is a section of the base of the sac at about the level marked b 

 in Fig. 2. The section is cut transversely through the neck of a pig 

 2 cm. long and passes through the larynx. It shows the relation of the 

 lymph heart both to the internal jugular vein and to the sterno-cleido- 

 mastoid muscle. The lining of the sac consists of a single layer of 

 endothelium. 



Fig. 1, which shows the lymph heart and 

 its ducts in a pig 2.7 cm. long, is to be com- 

 pared with Figs. 1 and 3 in this journal, 

 Vol. Ill, 1904, pp. 184 and 185, which show 

 the superficial lymphatics in pigs 2.5 cm. 

 and 3 cm. long. 



From these three figures it can be seen 

 that the lymph ducts or capillaries grow 



J, ,, " J, ,, n , , ii 1 • I'lG- 2. Diagram showing- the 



irom the apex Ot the sac first to the Skm relation of the lymph heart, of 



of the shoulder and back of the head. Then hea'rt'is in soiid^bfacii. '!i,^apex 



-, , „ -, p ., „ ,, of the lymph heart: b, base of 



ducts grow forward from the apex ot the sac the lymph heart; ejv, external 



, , .. I? , 1 , 1 ■ T . • 1 jugular vein : /i\ facial vein ; 



over the surface of the sterno-cleido-mastoid O'l', internal jugular vein, 

 muscle, and form a long plexus around the 



external jugular vein parallel to the anterior border of the muscle. This 

 plexus is shown in a little later stage in Fig. 6, and in section in Fig. 5. 

 From this long plexus ducts first grow to the face as is shown in Fig. 2, 

 Vol. Ill, p. 185. Later on it will be shown that at this stage, namely, 

 when the pig is 3 cm. long, the apex of the sac begins to be transforined 

 into a lymph node. 



The condition of the lymphatic system in the neck of a pig 3 cm. long 

 is as follows: There is first the lymph heart with its efterent ducts con- 

 nected with the veins; then ducts have grown from the apex of the sac 

 first to the skin of the shoulder and back of the head, and secondly to the 

 face. The sac shows also the first rudiments of a lymph gland. 



The maximum size of the lymph heart is attained when the pig is 

 3.6 cm. long, and in Fig. 4 is given a flat reconstruction of the sac at 

 this stage. It was made from a set of serial sections and gives the size 

 more accurately than the potash specimens. Fig. 5 is a section from the 



