THE SKULL. 579 



intervention of the hyoid. The latter mode of attachment is 

 called by Huxley autostylic. It is found in Holocephala, 

 Dipnoi, Amphibia and the Amniota. 



Teleostei. In addition to that of Elasmobranchii, the skull 

 of the Salmon is the only hyostylic skull in which, by the admi- 

 rable investigation of Parker (No. 451), the ontogeny of the hyoid 

 and mandibular bars has been satisfactorily worked out. Apart 

 from the presence of a series of membrane bones, the deve- 

 lopment of these bars agrees on the whole with the types already 

 described. 



The hyoid arch, though largely ossified, undergoes a process 

 of development very similar to that in Raja. It is formed as a 

 simple cartilaginous bar, which soon becomes segmented longi- 



, a I..? sp.o 

 ,t.0o. f n -9 



F' G - 335- YOUNG SALMON OF THE FIRST SUMMER, ABOUT 2 INCURS LONG ; 



SIDE VIEW OF SKULL, EXCLUDING BRANCHIAL ARCHES. (From Parker.) 



The palato-mandibular and hyoid tracts are detached from their proper situations, 



a line indicating the position where the hyomandibular is articulated beneath the 



pterotic ridge. 



ol. olfactory fossa; c.tr. trabecular cornu; /". itl*. upper labial cartilages ; p.s. 



presphenoid tract; t.cr. tegmen cranii ; s.o.b. supraorbital band; fo. superior fonta- 



nelle; n.c. notochord; b.o. basilar cartilage; /;-. trabecula; p.c. condyle for palatine 



cartilage; 5. trigeminal foramen ; "ja. facial foramen; 8. foramen for glossopharyngeal 



and vagus nerves; mk. Meckelian cartilage; op.c. opercular condyle. 



Bones: c.o. exoccipital; s.o. supraoccipital; e.f. epiotic; pt.o. pterotic; sp.o. 



sphenotic; op. opisthotic; pro. prootic; b.s. basisphenoid ; al.s. alisphenoid; o.s. 



orbitosphenoid ; I.e. ectethmoid or lateral ethmoid; pa. palatine; pg. pterygoid ; 



m.pg. mesopterygoid ; mt.pg. metapterygoid ; qu. quadrate; ar. articular; h.m. 



hyomandibular; sy. symplectic ; i.h. interhyal ; ep.h. epiceratohyal ; c.h. ceratohyal ; 



//.//. hypohyal; g.h. glosso- or basihyal. 



37? 



