86 F. W. THYNG 



channel with the terminal part of the subclavian vein at about 

 the same level. The connection with the internal jugular is 

 (usually) temporary, in which case the communication with the 

 subclavian represents the future permanent outlet of the adult 

 vessel. Sometimes a reverse condition occurs. Distally each 

 external jugular vein is connected through a capillary plexus, 

 caudad of the fossa conchae (shown, in part, in plate 5) with the 

 linguo-facial vein and its tributaries from the hyoid arch. 



The cephalic vein (Vxeph.) of which only a part is represented 

 here, occupies the radial border of the arm, and passes super- 

 ficial to the clavicle (which is just beginning to ossify) to join 

 the external jugular. A similar condition of this vein has been 

 represented for a human embryo of 22.8 mm. by Lewis ('09, fig. 

 4), and for a human embryo of 20 mm. by Evans ('12, fig. 478). 

 The portion of the cephalic vein superficial to the clavicle {V.jug.- 

 ceph.) has been named the jugulo-cephalic vein. It usually 

 atrophies since the cephalic commonly acquires a new connection 

 with the axillary. The jugulo-cephalic occasionally persists in 

 the adult, in which case the cephalic remains partially or entirely 

 tributary to the external jugular vein. 



The proximal end of the external jugular vein receives ven- 

 trally the anterior jugular vein (plat»e 5), proceeding from a 

 superficial venous plexus of the neck. A similar venous con- 

 nection between the external and anterior jugular veins has been 

 represented in a human embryo of 22.8 mm. by Lewis ('09, fig. 

 4). Since the anterior jugular vein is in the adult normally a 

 tributary of the external, it may be supposed that that part of 

 the external jugular vein which now opens into the internal 

 jugular, finally becomes the terminal part of the anterior jugular. 



Posterior cardinal system. The primitive posterior cardinals 

 " in great part have lost their identity since they have been reduced 

 to sinusoidal channels by the developing Wolffian bodies. These 

 channels, some of which gain prominence have been reduced fur- 

 ther or interrupted by the developing metanephros and supra- 

 renal gland. 



Minot ('98) demonstrated that the posterior cardinal veins in 

 pig embryos become subdivided by the mesonephric tubules into 



