22 



HIGH SCHOOL ZOOLOGY. 



the former terminating anteiuorly in a notch, the latter posteri- 

 orly in a bifid spine. Four projections mark each lateral border 

 of the skull, belonging to the mesethmoid, the parethmoid, the 

 sphenotic and the pterotic l)ones, Avliilo the hinder border pre- 

 sents a projection from the epiotic on either side of the snpra- 

 occipital s])ine. Thus twelve bones enter into the formation of 

 the ci-anial box, for all of the above-mentioned l)ones are in 

 pairs witli the exception of the mesethmoid and supra-occi[)ital. 



LS. On the floor of the skull (Fig. 7) the mesethmoid still forms 



Fig. 7. — Cranium and Anterior Vertebr.-e of Catfish, from below. 



Pm, premaxila ; m, niesethmoirl; v, vomer; pa, |)arethinoiil; o, orl)itosiihenoi(l ; f, 

 frontal; ps, parasphcnoiil; a, alisphenoid; pr, prooiic; h, articular surface for hyoman- 

 dibular on sphen- and pterotics ; b, liasioccipital with exoccipitals on either side; 

 s, supr.aclavicle ; ni, " malleus ;" 4, 5 and G, transverse processes of 4th, 5th and Cth 

 vertebrae. 



