TAIL-REGIOX OF POLISTOTKEMA (bDEIXOSTOMa) STOUTf. 317 
and the caudal vein. Concernins: their size, ench exceeded 
the calibre of the caudal artery. In the region of the lateral 
process of the median ventral cartilaginous bar the paired 
trunks unite in a common stem (Figs. 2, 4, and 4 a, L. H^e. 
T. (1 ), which soon bends ventrad between the two forks of 
the caudal vein, and when immediately above the narrow re- 
stricted portion of the ventral bar that is directly behind the 
lateral processes it trifurcates. Two lateral branches (Fig. 4 a, 
L. L. Hfe. T. 1 ) continue ventrad across the lateral 
surface of the narrow restricted portion of the median 
ventral bar immediately behind the lateral processes ; 
while an anterior branch (Fig. 4 a, A. L. H^e. T. j ' passes 
at first cephalad and then ventrad to curve around in 
front and between the lateral processes of the median ventral 
bar, where it receives the vential or inferior longitudinal 
hjemal lymphatic trunk (Fig. 4 a, J~ L. Hse. T. , and at 
this point of union there is a reservoir of considerable size, 
which to a considerable extent in the 10 cm. series but not 
at all in the 85 mm. series) overlaps the sides of the lateral 
processes. Immediately below the lateral processes and the 
restricted portion of the median ventral bar these three 
branches reunite in a common stem, which terminates in the 
ventral veno-lymphatic trunk directly in front of the caudal 
heart. A transverse section (as Fig. 3 sometimes shows one 
of the longitudinal Inemal lymphatic trunks to be p>aired, 
while another will show it single. 
Throughout its course the longitudinal lijemal lymphatic 
trunks receive at regular intervals the intersegmental 
heemal lymphatic trunks (Figs.3 and 4 a, T.j coming 
up from between each set of uivotomes. They always accom- 
pany a corresponding artery or vein, sometimes lying in front 
of it and again behind. As a rule between one pair of 
myotonies there would be an artery and a lymphatic vessel, 
and between the next pair a vein and a lymphatic vessel ; 
there being, then, double the number of lymphatics as arteries 
or veins, or the same number as arteries and veins 
taken together. In case of some of the piosterior ha?mal 
