Diagrams of the head of the main groups of Vertebrates 



Prostomiu 



I I I I I I I 



olf . W, 



P=..o-.yz 



The shaded squares are somites producing myotomes, the blaiil< squares, somites 

 not doing so. The hypoglossus roots on the whole correspond to the myotomes 

 from which the hypobranchial musculature is formed; the root belonging to the 

 last epibranchial somite, however, never forms part of the hypoglossus. 



a. p. animal pole, can. med. medullary tube, cr. cranio-vertebral limit. (Sc. in 

 Scylliuiii, Ac. in Acanthias], gr. H. groove of Hatschek, m. mouth, near. a. 

 neural archs, np. neuropore, o. auditory vesicle, oc. eye, ore. a. occipital arch,, 

 ol(. olfactory groove, pr. mand. "praemandibular somite", sp. spiracle. 



