THE MUSCULAR SYSTEM 

 I5T SOMITE 



ANTERIOR 

 CAVITY 

 ENDOSTYLE 

 CLUB-SHAPED GLAND 



A. AMPHIOXUS EMBRYO 



OMfTE 10 



1ST PERM. GILL-SLIT 



209 



FACIALIS GANGLION OTIC CAPSULE 

 1ST SOMITE 



LENS, 



SOMITE 10 



THYROID 

 ST PERM.GILL-SUT 



B. PETROMYZON 



VI 



FACIALIS GANGLION 

 1ST SOMITE 



SOMITE 10 



ANTERIOR CAVITY 



HEART 



C.SQUALUS 



Pig. 197. — Diagrams of the mesodermal (somatic) segmentation in the head region 

 of embryos of lower chordates as viewed from the left side. In embryos of these lower 

 vertebrates, just as in the adult Amphioxus, the somites (myotomes) extend in 

 unbroken succession throughout head and trunk. Roman numerals number the brain 

 " neur omeres . " 



