96 OTTO F. KAMPMEIER 
multiple junction and the amalgamation of the other channels 
into a larger one: secondly, the outgrowth of the anterior verte- 
bral vein (v. vert. ant.) just internal to the latter, and, thirdly, 
the distention of the lymph-heart cavity, the bulging of which 
is more pronounced laterally than medially where the myotomes 
resist its expansion (ef. photomicrographs figs. 18 to 22). Asa 
result of the interaction of these factors, the lymphaticovenous 
.tap is shifted forward and medially. The ultimate condition has 
not yet been attained, however, for in the young toad the junction 
is at the anterior, more conical, end of the heart (fig. 24). Be- 
tween the stage figured in figure 35 and the final one, it is evident, 
therefore, that considerable displacement still occurs, but to 
specify all of the underlying causes is impossible and is of little 
importance. Unquestionably, it is correlated with the stresses 
and strains due to other bodily changes that take place in the 
neighborhood of the lymph heart during development, such as 
the atrophy of the pronephros and the proximal segment of the 
posteardinal,'® the absorption of the pronephric sinus by the 
internal jugular, the consequent shifting of the mouth of the 
anterior vertebral vein, the differentiation of the myotomes, and 
the rearrangement of the resulting muscles, to mention only a few 
of the most evident modifications. 
Histogenesis 
a. The lymph heart wall. Waving described the conformation 
of the lymph heart and its venous relations, the development of 
its walls and valves remains to be discussed. 
In early stages (4- and 5-mm. embryos) when the anterior 
intersegmental vessels have just been established, the area 
between the epidermis and the myotomes is very narrow, not 
much wider than is sufficient to accommodate these vessels 
(fig. 15). The mesenchyme, too, is very scanty here except in 
the region of the 3rd intersegmental vein, where its yolk-laden 
cells soon become more numerous and are locally massed against 
16'The medial division of the postcardinal vein has been shown by the writer 
(Anat. Rec., vol. 19, 1920) to correspond to the sub-cardinal vein of higher verte- 
brates. 
