WordNet
haemal arch
n. a structure arising ventrally from a vertebral centrum and enclosing the caudal blood vessels [syn: hemal arch]
Wikipedia
Haemal arch
A haemal arch is a bony arch on the underside of a tail vertebra of a vertebrate.
The hole so formed is the haemal canal.
It sometimes has a haemal spine on.
The blood vessels to and from the tail run through the arch.