# Page:Philosophical Transactions - Volume 096.djvu/16

The dorsal series (${\displaystyle ff}$) arises from the back of the head. In its course it is terminated on the upper edge by the bones, which support the single fins, and a membranous septum: at this part the flakes are thin. Its lower margin is bounded by the vertebral series, where the flakes become gradually thicker. The first flake is composed of longer fibres than the rest, and possesses more red blood. Those succeeding it