266 



COMPARATIVE ANATOMY 



FACIALIS GANGLION qTIC CAPSUL f 



MYOTOME 3 ^ tAPSULt 

 MYOTOME 2 

 MYOTOME I. 



MYOTOME 



MYOTOME 2 



A. PETROMYZON. 



FACIALIS GANGLION 

 MYOTOME JV 

 MYOTOME 2 

 MYOTOME 



HYPOBRANCHIAL MUSCLE 

 1ST PERM. GILL-SLIT 



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. 220. — Diagrams based upon cyclostome and elasmobranch embryos illustrating 

 the phylogenesis of the six eye muscles. 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. 



