479 
extended originally throughout the whole of the region in question, 
but that posteriorly the superficial vessel has disappeared on the right 
side and the deep vessel on the left. Further back the “right anterior 
cardinal” slips between the constrictor pharyngis and the posterior 
portion of the longitudinalis linguae muscles, to anastomose with the 
inferior jugular vein (10), which it does by bending round ventrally 
until it takes up a median ventral position just behind the club muscle. 
The inferior jugular finally crosses the middle line to the left side 
to open into the sinus venosus. It is of course possible that the in- 
ferior jugular represents the fused deep cardinals of both sides. Its 
formation and variations suggest a left as well as a right factor, 
although I have never found it actually connected with the left cardinal 
system. In Petromyzon the corresponding vein does arise by the 
fusion of paired vessels. 
The so-called “anterior portal vein” of Jackson (7) is beyond 
question the posterior section of the right anterior cardinal system. 
It corresponds in every respect with the left anterior cardinal vein. 
It arises by the union of the dorsal and ventral factors of a segmental 
vein just behind the region where the anterior section of the “right 
anterior cardinal” bends ventrally to anastomose with the inferior 
jugular vein. The posterior extension of this vessel (7°) behind its 
connection with the portal heart (7) was not noticed by JACKSON in 
Bdellostoma, and is interesting as representing perhaps the remains 
of the right Cuvierian duct, although its posterior opening into the 
portal vein is unexpected. In one injected specimen, however, a con- 
nection with the left Cuvierian duct was actually found. The right 
anterior cardinal communicated with the portal vein as described 
above, but shortly behind the pronephros it detached a small vessel 
which opened into the common posterior cardinal vein immediately 
cephalad of the junction of the right and left posterior cardinals. 
The right and left anterior cardinal veins are connected by a well- 
marked anastomosis (6) in the neighbourhood of the heart. In two 
dissections this anastomosis was really a very irregular sinus connected 
by large openings with both anterior cardinal veins. I saw no valves. 
The presence of this anastomosis is doubtless associated with the loss 
of the right Cuvierian duct. 
Apart from the skin and brain, the connection between the arteries. 
and the veins in front of the auditory capsule is by means of veno- 
lymphatic lacunae. 
