LYMPHATICS IN FROG LARVAE 79 



vein, and in no sense a vein of the lateral line, as has been 

 assumed. 



Tributary veins from the neural plexus are seen in figure 

 37, running out into the first and second veins, as in earlier 

 injections (figs. 1 and 2), but the more peripheral vessels, 

 which are now also effective in maintaining these anterior 

 veins, are only partly injected in this specimen. The main 

 stem alone of the cutaneous artery, which supplies the periph- 

 eral plexus, appears as it curves back over the anterior sur- 

 face of the pronephros; and some of the network of the 

 proximal plexus of the first vein which receives the facial 

 connecting vein is well shown. This is the earliest injection 

 obtained of the connecting vein from the maxillary plexus of 

 the face. It over-arches the branchial region in its passage 

 to the first intersegmental vein. 



The anterior lymph heart on the third vein (fig. 37) locates 

 the central end of the lymphatic system, and with this as a 

 guide, together with the veins introduced in corresponding 

 pictures of lymphatics, it will be possible to understand the 

 relations to the veins of the lymphatics shown in figures 2 to 8 

 of this period. 



In stages following the second period the increased flow of 

 blood from the cutaneous artery is accompanied by extension 

 and enlargement of vessels in both the anterior vertebral and 

 great cutaneous plexuses. 



This is conspicuous in figure 38, where the proximal veins 

 of the plexuses fed by the great cutaneous artery which 

 emerges just in front of the pronephros, hang over the gland 

 in wide loops. The artery divides into two branches, which 

 spread forward and back in the dorsal body wall ; the anterior 

 branch, associated with the plexuses of the anterior segments 

 and with the facial connecting veins ; while the posterior divi- 

 sion has already formed a wide-open plexus lateral to seg- 

 ments as far back as the base of the tail. The great abdominal 

 vein runs vent rally from the anterior lateral margin of the 

 plexus ; while the vessels of the net converge medially to join 

 the dorsal loops of the first three intersegmental veins over 

 the edges of the anterior muscle segments. 



