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Univcrsify of California Puhlications in Zoology [Vol. is 



latero-veiitral as having two laj^ers. Maurer (1912) in working on 

 the trunk musculature of a number of selachians finds that layer- 

 formation occurs in Mustelus, but not in Scyllium, Sphiax, Acanthias, 

 and others. 



In Heptanchus maculatus the body musculature (figs. 10, 11, 12) 

 is divided by the lateral septum into dorsal and ventral parts. These 



m.d. 



Fig. 10. Cross section in trunk region, Heptanchus maculatus (X %.). 

 h.c, body cavity; /., lateral nniscle bundle; la. v., lateral vein; }.d., latero- 

 dorsal muscle bundle; /. ?., lateral line; /. v., latero-ventral muscle bundle; m. d.. 

 medio-dorsal muscle bundle; m. v., medio-ventral muscle bundle. 



longitudinal muscles extend from the cranium to the tip of the tail. 

 Dorsal to the lateral septum there are three muscle bundles, the lateral, 

 latero-dorsal, and medio-dorsal. Ventral to the septum are the latero- 

 and medio-ventral parts. The dorsal part is attached anteriorly to 

 the cranium and to the pectoral girdle, the ventral part to the pectoral 

 girdle. The hypobranchial muscles previously described form an 

 anterior ventral specialization of these latter muscles. The longi- 



