110 OTTO F. KAMPMEIER 
2. On the development of the jugular lymphatic 
In 5- to 6-mm. embryos, the first three intersegmental veins, 
which are dorsal vertical tributaries of the pronephric venous 
sinus (common segment of pre- and postcardinal veins), become 
joined longitudinally by imteranastomoses and consequently 
take on a plexiform character. 
The aforesaid intersegmental vein plexus, which in view of its 
original relations and its future function may be called a veno- 
lymphatic one, gives rise to the jugular lymphatic, the important 
change consisting in its gradual separation from the veins (pro- 
nephric venous sinus). 
By the expansion, approximation, and fusion of the longi- 
tudinal components of the plexus, the main channel of the jugular 
lymphatic is definitely established, and it eventually makes con- 
nection -anteriorly with the temporal division of the primary 
maxillary lymph sinus and at its posterior end, in common with 
the lateral line lymphatic, joins the anterior lymph heart. 
3. On the development of the anterior lymph heart 
The anterior lymph heart, on either side, arises from a cir- 
cumscribed portion of the venolymphatie plexus, mentioned in 
the preceding section, at the level and in the axis of the original 
3rd intersegmental vein. 
The plexiform anlage of the lymph heart becomes transformed 
into the uninterrupted heart chamber by the expansion and fusion 
of its interjoied channels. 
The developing lymph heart in approximately 7- or 8-mm. 
embryos severs connection with the cireumjacent venolymphatic 
plexus, but remains in continuity with the venous system via 
the mouth of the former 3rd intersegmental vein, now the mouth 
of the anterior vertebral vein. 
A communication is reestablished between lymph heart and 
afferent lymphatic, the common segment of the jugular and 
lateral-line lymphatics, in approximately 10-mm. embryos; this 
is accomplished by the gradual approximation of the two struc- 
tures, due to their growth and dilatation, and by the perforation 
