Motor System — Muscles and Skeleton 



121 



POSTFRONTAL 



EXOCCIPITAL 



SUPRAOCCIPITAL 



Fig. 119. (Top) The head of a sturgeon, viewed from above as a translucent 

 object. Membrane-bones (scutes) are outlined, and the inner cartilaginous cranium 

 stippled. Comparative anatomy identifies certain scutes as homologs of bones in 

 the mammalian skull. (After Gegenbaur. Courtesy, Neal and Rand: "Chordate 

 Anatomy," Philadelphia, The Blakiston Company.) 



(Bottom) Skull of an ancient stegocephalan amphibian {Capitosaurus). (Eo) 

 Exoccipital; (Ep) tabulare; (F) frontal; (Ju) zygomatic (jugal); (La) lacrimal; 

 (Mx) maxilla; (Na) nasal; (0) orbit; (Pa) parietal; (Pmr) premaxilla; (Por) post- 

 orbital; (Prf) prefrontal; (Ptf) postfrontal; (Qj) quadratojugal; (So) dermoccipital; 

 (Sq) squamosal; (St) supratemporal. (After Zittel. Courtesy, Kingsley: "Com- 

 parative Anatomy of Vertebrates," Philadelphia, the Blakiston Company.) 



