90 



Basic Structure of Vertebrates 



A.AWPHIOXUS. 



\ ' | ' ATRIOPORE 



METAPLEURAL FOLD \|/ LATERAL TRUNK CSOMATIO MUSCLES 

 GONADS 



HYPOBRANCHIAL MUSCLE 



B. PETROMYZON. 



LATERAL TRUNK MUSCLES ANUS 



EPAX1AL TRUNK MUSCLES 



•>•;- 



HYPAXIAL MUSCLES 



.-ANAL ORIFICE 



Fig. 88. The lateral trunk muscles of a cephalochordate, a cyclostome, and an 

 elasmobranch, showing their striking metamerism and fundamental similarity. 

 (A) Amphioxus. (B) Petromyzon (lamprey eel) (C) Squalus (dogfish). (Courtesy, 

 Neal and Band: "Chordate Anatomy," Philadelphia, The Blakiston Company.) 



Fig. 89. Scheme of arrangement of myomeres and muscle-fibers in (A) Petro- 

 myzon, (B) elasmobranch, (C) teleost, and (D) urodele. (eop, eos) Deep and super- 

 ficial external oblique; (io) internal oblique; (1) longissimus dorsi; (r) rectus abdom- 

 inis; (t) transversus; (v) subvertebral. (Courtesy, Kingsley: "Comparative Ana- 

 tomy of Vertebrates," Philadelphia, The Blakiston Company.) 



