The posterior (terminal) vertebral segment (or segments), located posterior to the last vertebra, which has a typical hemal arch. (Urostyle). The urostyle actually consists of one (or more) reduced vertebra. i. e. a vertebral center (one or more), lacking a hemal arch and with it a hemal canal. The arteria caudalis splits anterior to the urostyle, one branch each runs to the hypural, bones attached ventro-posteriorly to the urostyle, which are supporting the finrays of the caudal fin. When counting vertebrae, the urostyle is considered to be a single element in the total count.
In the Osteoglossomorpha the urostyle is not typically developed, it is represented by the ural vertebra, which are only somewhat reduced and bear the hypurals. (Tail skeleton )