LYMPHATICS IN FROG LARVAE 21 



(Kampmeier, '22) from a reconstruction of this region offered 

 as a primary stage of the lymphatic system in the toad embryo. 



The injected submaxillary plexus (Sx.Plx.) in our figure la 

 shows much the same general arrangement as the reconstruc- 

 tion, though important vessels are omitted in the latter. The 

 vessels are grouped on either side of the thyroid in a rather 

 close network, with the external jugular veins well defined on 

 the medial edges passing back on either side of the heart to 

 join the duct of Cuvier. Laterally the net is somewhat looser, 

 more open. There is a tendency in places for the vessels to 

 crowd into deep and superficial groups. 



The submaxillary plexus is seen clearly through the inner 

 portions of the suckers in both reconstructions and injections, 

 ventral and superficial to the aortic arches, with the external 

 carotid arteries deep to it running forward from the first 

 arch to supply the anterior extremities of the network. 



This completes the picture of the plexus as described for 

 the toad, except that small vessels are added by Kampmeier 

 at the lateral margins of the reconstruction. He colors these 

 vessels differently from the others, to represent detached lym- 

 phatic rudiments, and believes that the presence of yolk gran- 

 ules in the walls is a distinguishing character. 



Extensive study of injections as well as of uninjected sec- 

 tions of frog embryos has failed to identify such detached 

 rudiments to be classed as part of the lymphatic system adja- 

 cent to the submaxillary plexus, and no specific relation of 

 yolk granules to the walls has been observed. The network 

 of blood vessels in figure 1 seems amply sufficient to account 

 for all vessels found. 



Further examination of injections reveals that the sub- 

 maxillary plexus is indeed more complicated than is indicated 

 in the reconstructions for the toad, and that more vessels 

 (blood vessels, not lymphatics) should be added to the latter. 



In addition to the external carotid arteries already described 

 as supplying the plexus, two more arteries are found in the 

 frog injections, entering from in front, one joining the ante- 

 rior angle on each side. 



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