118 
JANE I. ROBERTSON. 
communicating with the ducts of Cuvier at their junction 
with the pronephric sinuses (posterior cardinal veins, Text- 
figs. 24 c and d, A. Card.), The anterior ends of these vessels 
bifurcate in the region of the eye, one branch being super- 
ficial, and one, the anterior cerebral vein, passing deeply from 
the front part of the head. As they pass backwards the 
anterior cardinal veins lie ventral to the otocysts and then 
curve inwards internally to the posterior cranial nerves, and 
then outwards again a little to reach the pronephric sinuses. 
Presently, however, a new vessel appears on either side below 
and slightly external to the otocysts. This new vessel arises 
from the anterior cardinal vein immediately anterior to the 
ganglion of the seventh and eighth cranial nerves, and, 
passing immediately external to it, joins the anterior cardinal 
vein again between the eighth and ninth nerves (Stage 30) 
A little later (Stage 31) the outer vessel grows further 
back externally to the ninth nerve, and then joins the anterior 
cardinal vein between the ninth and tenth nerves, while 
finally (Stage 31-J-) it extends backwards external to the 
tenth nerve and joins the anterior cardinal vein behind it. 
Meanwhile, as each fresh segment of this lateral cephalic 
vessel develops, the corresponding stretch of anterior cardinal 
vein (median cephalic) disappears from before backwards 
(Text-fig. 24 E, M. C.). The posterior part of the third seg- 
ment of the median cephalic persists, however, in the adult 
as a short wide vessel between the skull and muscles of the 
head, opening with the posterior cerebral vein from the in- 
terior of the skull, into the lateral cephalic vein behind the 
otocyst. Finally, the lateral cephalic vein passes below the 
otocyst and external to the cranial nerves, being continuous 
with the anterior cardinal vein in front of and behind them 
and forming to all appearances simply a portion of the 
anterior cardinal. In Lepido siren therefore, while the 
main features of the development of the anterior cardinal 
veins are the same as for all vertebrates, the details 
tally closely with those given for the same vessels in 
Tropidonotus ( 10 ). 
