/.'. Sabin. 



the third, fourth ami fifth segmental veins, thai is the 

 lymphatic a 



• ■ the lymphatic area definitely it is neeessan to noti 

 details "t' the superficial veins more carefully. The superficial plexus 

 ateral groove is finer meshed and of smaller capillaries than 

 • -•. The groove is an important land mark and it shows best in 



i, fig. 'i. From the plexus in the groove a -I i of wide 



lillaries i< growing dorsalward external to the myotomes, ami loops 

 from this sheel connect with 'lie deep plexus around the spinal cord. 

 The -kill over the entire dorsal surface of the cord i- an entirely non- 

 ular area at tl . From the ventral border of the super- 



ficial plexus in the groove a sheet of wider and more opi Q-meshed capil- 

 laries covers the surface of the embryo over the anterior cardinal 

 I i - rfaci contour of this, the lymphatic area, is a swelling 

 i in fig. 6, which 1 shall call the jugular lymphatic ridge. T • 

 blood capillaries of this area are very superficial ami drain into the 

 cardinal vein in four ways: ( 1 ) Through the plexus in the groove ami 

 it- dorso-latera] superficial veins: ( ".' ) in .-mall pari through direct 

 branches t" the lateral surface of the cardinal vein; (.'!) through 

 branches of the ventro-lateral surface of the anterior cardinal vein 

 which drain the pericardium ( lie.. •">): ami (I) through anastomoses 

 with the capillaries (fig. 5 > of the primitive ulnar vein. The primi- 

 tive ulnar vein has developed from the diffuse capillary arm bud 

 plexus of the preceding stage. It enters the lateral surface of the 

 sterior cardinal vein directly opposite the fifth segmental branch. 

 Thus a part of the blood <>i' the branchial region and of the pericar- 

 dium drains through the superficial plexus over the lymphatic ridge 

 rimitive ulnar vein, [n a little older embryos, namely, those 

 12 mm. long, a ■' vein has developed from the arm bud plexus 



jusl alward to the primitive ulnar, which now receives the hi 1 



'ii the plexus of the lymphatic ridge. The complete description of 

 this superficial plexus involves a study of the origin of the external 

 jugular vein which I do no! wish to go into until I can illustrate it 

 adequately. I bring up the point here because A. II. (lark (24) has 

 -hewn thai occasionally a lymph trunk in the neck in older pigs opens 

 directly into the externa] jugular vein near its point of union with the 

 internal jugular vein. It is therefore of importance to note that the 

 capillary plexus in the arm bud, from which this pan of the internal 

 jugular vein comes, i- presenl in the embryo when the lymphatic- an 



,AW~ 



mvt Of I 



