neural tube 

 myotome /C^ ^^^ notochord 

 myocoel 



coelom 



sclerotome (filled in sclerocoel) 



epaxiol muscle 

 dermatome 

 horizontal septum 

 hypaxial muscle 



nephric tubule 

 coelom 

 gut 



metapleural fold 



B C 



AMPHIOXUS 



D E 



GNATHOSTOME 



Figure 14-1. Four stages (A-D) of coelomic pouch differentiation in Amphioxus os compared witfi 

 mesodermal differentiation in a gnathostome (see also Figure 10-15). (A to C after Prenant, 1936) 



A AMPHIOXUS 



B 



LAMPREY 



muscle 



SHARK 



D SALMON 



Figure 14-2. Shape of an individual myomere in four chordotes. (A after Nishi, 1938; C after 

 Coles; D ofter Greene and Greene, 1913) 



eye muscle somites l-lll 



endolymphatic duct 



otic vesicle ^ ^^ permonent myotome (7th) 



myotomes 



pectoral fin muscle buds 

 hypobranchiol muscle buds 



forebroin 



pharyngeal pouches 1-6 



Figure 14-3. Origin of the hypobranchiol musculature in a shark (gnathostome). (After Romer, 

 1955) 



SKELETAL MUSCULATURE • 421 



