. The elasmobranch fishes . THE ELASMOBRANCH FISHES 97 region of the skull to the tip of the tail. These fillers universally take a horizon- tal direction. Those fibers between the lateral line septum and the midventral line are divided into a lateral () and a ventral () region. The lateral muscle () is readily recognized by the fact that it lies just ventral to the lateral line and is of a dark color. Between pelvic and pectoral regions this bundle is folded in in such a way (figs. 99 and 100) as to be overlapped by the ventral bundle (). Anterior to the pelvis the fibers in t
. The elasmobranch fishes . THE ELASMOBRANCH FISHES 97 region of the skull to the tip of the tail. These fillers universally take a horizon- tal direction. Those fibers between the lateral line septum and the midventral line are divided into a lateral () and a ventral () region. The lateral muscle () is readily recognized by the fact that it lies just ventral to the lateral line and is of a dark color. Between pelvic and pectoral regions this bundle is folded in in such a way (figs. 99 and 100) as to be overlapped by the ventral bundle (). Anterior to the pelvis the fibers in the lateral bundle may take an almost horizontal direction (, fig. 112) but they usually take an oblique direction of anterior and upward (fig. 100); while posterior to .^''-'r'^''^f^i^'. the pelvic area the fibers of this bundle run more or less horizontally. The ventral bundle {,^gs. 100 and 112) is highly specialized and its fibers take a characteristic anteroventral di- rection. In some of the Elasmobranchs, as in Zygaena, the ventral bundle is further specialized into a rectus ab- dominis at the midventral line (, fig. 100). Figure 99 is a model for Squalns siickUi of all muscle fibers between two myosepta in the region of the first dor- Tig. 98. Showing the finer anatomy of de- , „ T^ m ., Ml 1 ,T , ,1 veloping muscle. (Modified from Erik sal nn. Dorsally it will be seen that the Miiiier.) septa run posteriorly close together and almost parallel with the middorsal line. They then turn anteriorly and run forward. Next they bend on an acute angle and curve backward; and then they turn forw^ard and downward to the lateral line, where they fold inward and are carried forward. When the septa emerge from the fold they are dis- placed backward so that as they pass through the lateral bundle they are fully a half-segment posterior to the same myosepta above the lateral line. In the lateral bundles the septa curve downward and backward and then turn for- ward where th
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