THE MUSCULAR SYSTEM 



197 



FACIALIS GANGLION 0^,^ CAPSULE 



MYOTOME 3 

 MYOTOME 2 

 MYOTOME I. 



MYOTOME 



MYOTOME 2 



A. PETROMYZON. 



HYPOBRANCHIAL MUSCLE 

 1ST PERM. GILL-SLIT 



FACIALIS GANGLION 

 MYOTOME 3V 

 MYOTOME 2 

 MYOTOME 



OTIC CAPSULE 



ST PERM. META-OTIC MYOTOME 



THYROID 

 ANTERIOR CAV. 



HYPOBRANCHIAL MUSCLE 



MYOTOME 



B. SQUALUS. 



SUP. RECTUS 

 SUP. OBLIQUE 



INT. RECTUS 



EXT. RECTUS 



1ST META-OTIC MYOTOME 



OLF. PIT 



INF. OBLIQUE 



INF. RECTUS 



C. ADULT SQUALUS. 



HYPOBRANCHIAL MUSCLE 



Fig. 186. — Diagrams based upon cyclostome and elasniobranch embryos illustrating 

 the phylogenesis of the six eye muscles. The eye muscles develop from the first three 

 embryonic myotomes. Myotomes are cross-hatched. Those which degenerate in 

 ontogenesis are cross-hatched with broken lines. In C the eye muscles are shown as if 

 viewed from the median side of the eye. 



