Approximating a semicircle with the greatest width near the center of the arc. Approximating a triangle. An upper jaw bone lying immediately above the main jaw bone, the maxilla. The lines of union between adjacent bony elements such as those found on the terminal hooks on the fourth ray of the gonopodium of some livebearers. A prominent bump in the middle of the lower jaw of some mullets.
T tail ridge a small raised crest found along the posterior sides toward the tail of pipefishes.
These are often found in association with anteriorly located trunk ridges. The angular bone on end of the fourth and fifth rays of the gonopodium of male livebearers. A thin elevated portion extending along the midline of pipefishes. The portion found along the midline anterior to the dorsal fin is called the median trunk ridge. In some species it dips ventrally at the anus and joins the posteriorally located inferior trunk ridge.