212 George 8. Huntington and Charles F. W. McClure 
and the most variable in form and composition of all the dorsal 
branches of this vein. It is formed by the confluence of two trunks 
(a and b) which, cephalad and caudad, follow the dorso-lateral 
border of the neural tube, and it opens into the precardinal by an 
enlarged and expanded base, frequently fenestrated, which re- 
ceives a large single cephalic tributary (4S in fig. 8). 
Preeardinal tributary 4 is on the border line dividing the series 
of the preceding branches 1, 2, and 3, uniformly involved to a 
greater or less extent in the development of the cephalic division 
of the ventral veno-lymphatic plexus, from the series of per- 
manent dorsal somatic tributaries of the promontory (5S, 6S, and 
7S, in fig. 8). Consequently, while 4 shares with the anterior 
branches 1, 2, and 3, the tendency to divide by enlargement of the 
plexiform terminal into a medial somatic and lateral veno-lym- 
phatic component, the tributary, as a whole, inclines in individual 
cases in one or the other of these directions, i. e., either toward 
the more complete veno-lymphatic or the dorsal somatic type of 
development. The genetic characters of 4 are more marked, com- 
pared with the preceding branches 1, 2, and 3, by reason of its 
large size and extensive drainage area. Certain instances, or 
rather certain developmental stages (cf. series 188, figs. 35, 37, 18 
and 114A), offer striking pictures of the separation into a dorso- 
lateral veno-lymphatic (4VL) and a dorso-medial somatic compo- 
nent (4S), connected by a number of transverse anastomoses. 
Further, in the same sense, the entire caudal division of the 
ventral veno-lymphatic plexus is interposed between the ceph- 
alic division of the same and the dorsal veno-lymphatic plexus, 
which is developed entirely from the promontory by condensation 
of the plexiform dorso-lateral cireumferemce of this segment of 
the main venous channel, without involving the promontorial 
dorsal somatic branches (5S, 6S, etc.). 
Hence the caudal division of the ventral veno-lymphatic plexus 
of the early stages inclines in some instances toward the develop- 
mental type of its cephalic associate, i. e., it involves dorsal 
somatic tributary 4 to a greater or less extent. In other cases 
it follows more closely in its development the succeeding dorsal 
veno-lymphatic plexus, i. e., it is derived largely or entirely from 
