. The Bashford Dean memorial volume :. Fishes; Sharks; Fishes, Fossil. 382 Bashford Dean lAemorial Volume. THE AXIAL MUSCLES In fishes the axial muscles comprise (a) the great masses of muscle contributing to the formation of the body wall and tail; (b) a group of muscles in the hypobranchial region; and (c) the muscles that move the eyeballs. Muscles of the Trunk and Tail.—Metamerism is such a striking feature of the trunk muscles of fishes that it overshadows the longitudinal division into muscle bundles or layers and the incipient diiferentiation into indi'V'idual muscles—a development that
. The Bashford Dean memorial volume :. Fishes; Sharks; Fishes, Fossil. 382 Bashford Dean lAemorial Volume. THE AXIAL MUSCLES In fishes the axial muscles comprise (a) the great masses of muscle contributing to the formation of the body wall and tail; (b) a group of muscles in the hypobranchial region; and (c) the muscles that move the eyeballs. Muscles of the Trunk and Tail.—Metamerism is such a striking feature of the trunk muscles of fishes that it overshadows the longitudinal division into muscle bundles or layers and the incipient diiferentiation into indi'V'idual muscles—a development that, in the higher vertebrates, quite reverses the picture. In surface views of the six large embryos of Chlamydoselachus in the American Museum, ranging from 190 mm. to 374 mm. in length, the myomeres are more or less sharply defined. Along the lateral surfaces of the trunk and tail they are clearly outHned, and in some specimens they may be traced ventrally as far as the tropeic folds. Dorsally, they are usually obscure and in this situation better views were obtained by removing patches of skin from one of these em' bryonic specimens. In the adult specimens, only slight indications of the body musculature could be seen until after the skin had been reflected; then the myosepta stood out boldly. It is ap' parent, even from a cursory study of our mate- rial, that the myomeres of the trunk region of Chlaynydoselachus conform to the primitive elasmobranch type and bear a close resemblance to those of Heptarichus as described and figured by Maurer (1912) and Daniel (1934). From Daniel (1934, p. 89) I quote the following para- graph which is illustrated by my Text-figure 53: In a side view, the muscles of the body oi Heptanchus maculatus axe divided at the lateral line (n.) into dorsal bundles () which attach to the cranium, and ventrolateral bundles which attach to the pectoral girdle. Both the dorsal and the ventrolateral muscles extend to the tip of the tail. In these bund
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