{214}[Illustration: FIG. 123.—A, view of the left side of the skull of a Salmon; B, the left half of the primary upper and lower jaws, and the hyoid arch. The cartilage is dotted. _an_, Angular; _ar_, articular; _b.hy_, basi-hyal; _br.r_, branchiostegal rays; _c_, cranium; _c.h_, cerato-hyal; _c.or_, circum-orbital bones; _d_, dentary; _d.eth_, dermal mesethmoid; _ep.h_, epihyal; _ep.o_, epiotic; _eth.p_, ethmo-palatine process; _f_, frontal; _h.hy_, hypo-hyal; _hym_, hyomandibular; _i.op_, inter-operculum; _j_, jugal; _mks_, Meckel's cartilage; _mpg_, mesopterygoid; _mt.pg_, metapterygoid; _mx_, maxilla; _n_, nasal; _op_, operculum; _op′_, condyle on the hyomandibular for the operculum; _orb_, orbit; _p_, parietal; _pa_, palatine; _p.mx_, premaxilla; _p.op_, pre-operculum; _pt_, pterygoid; _pt.o_, pterotic; _q_, quadrate; _so_, supra-occipital; _s.op_, suboperculum; _sp.o_, sphenotic; _s.t_, supra-temporal (or squamosal); _st.hy_, stylo-hyal; _sy_, symplectic; _u.l.c_, _u.l.c′_, upper labial cartilages; _u.l.c^2_, second upper labial. (From W. K. Parker.)] The hinder part of this is ossified to form the _articular_, which has a deeply concave surface for articulation with the quadrate; and below this there is a small membrane bone, the _angular_. The rest of the cartilage is partially {215}ensheathed on its outer side by a large tooth-bone, the dentigerous _dentary_. The hyoid arch is similar to that of the Dog-Fish, except that its primitively cartilaginous segments are almost completely ossified (Fig. 123, B). The large upper segment or _hyomandibular_ bone articulates mainly with the pterotic, but partly also with the sphenotic element of the periotic capsule; below it is connected with a slender _symplectic_ bone, and from the cartilage connecting the two depends the rest of the hyoid arch, consisting in succession of _stylo-hyal_, _epi-hyal_, _cerato-hyal_, and _hypo-hyal_ bones, with a median teeth-bearing _basi-hyal_. The palato-pterygo-quadrate bar has no direct connexion with the skull, except anteriorly where its palatine element articulates with the lateral ethmoid. The real suspensorium is formed by the hyomandibular and symplectic bones, to which the hinder margins of the quadrate and metapterygoid bones are rigidly attached by suture, hence, as in the Dog-Fish, the skull is hyostylic. Behind the hyoid arch there are five branchial arches, which generally resemble those of the Dog-Fish, except that their component segments are ossified as cartilage bones.