SKULL 



267 



sharing in the protection of the horizontal semicircular canal and 

 the posterior vertical canal. This epiotic, like the opisthotic and 

 prootic, arises in close relation with the cartilage, and probably 

 has never been superficial. The prootic (petrosum) occupies 

 the anterior ventral region of the auditory capsule, generally 



elk 



pmsc. 



FIG. 236. 



Dorsal view of the skull of Amia calm, L. (After Allis.) The course of the lateral-line<system 

 is indicated by a dotted line on the left side, an, adnasal ; d, dentary ; eth, mesethmoid ; 

 /, frontal ; I, lachrymal or first suborbital ; na, nasal ; op, opercular ; p, parietal ; pmsc, 

 premaxilla ; pobd and pobv, dorsal and ventral iK>storbitals ; pop, preopercular ; pp, supra- 

 temporal ; pt, post-temporal ; s, pterotic. ; so, suborbitals. 



surrounds the exit of the facial nerve, and lodges the anterior 

 semicii-cular canal. The opisthotic (intercalare), situated behind it, 

 may cover the outer horizontal canal ; but is often small, and 

 sometimes absent (many Teleostei). As Huxley showed [229], 

 the number and disposition of these ' otic ' bones is very constant 

 among Teleostomes, and many if not all of them can be identified 

 in the terrestrial Vertebrates. 



