Mv. T. H. Hvixlcy on the Theory of the Vertebrate Skull. 4.29 



distinct and separate portions — the anterior division V-shaped, having 

 its anterior cms fixed and its posterior cms free above ; the posterior, 

 stylitbrm, parallel with the posterior leg of the V, and free below. 

 The anterior division supports the mandibular cartilage, the pos- 

 terior the hyoidean coruu. 



As ossification takes place, that part of the anterior crus of the 

 V-shaped cartilage which is attached to the ethmo-presphenoidal car- 

 tilage becomes the j)alatiiie ; its angle becomes the ji((jal ; between 

 these two the transverse and pterygoidien (represented by only one 

 bone in Gasterosteus) are developed in and around the anterior 

 crus : the tympanal arises in the same way around the free end of 

 the posterior crus. Thus these bones constitute an assemblage 

 which is at first quite distinct from the other elements of the sus- 

 pensorium, and immediately supports the mandibular cartilage. 



The proximal end (II. M.) of the posterior styliform division gradu- 

 ally becomes articulated with the cranial walls, and, ossifying, is con- 

 verted into the temporal. The distal cylindrical end (S.Y.) becomes 

 surrounded by an osseous sheath, which at first leaves its distal end 

 unenclosed. The bone thus formed is the symplectique, which is at 

 first free, but eventually becomes enclosed within a sheath furnished 

 to it by the Juyal, and so strengthens the union of the two di^-isions 

 of the arch already established by the junction of the tyynjjanal with. 

 the temporal. The symplectique and temporal do not meet, but leave 

 between them a cartilaginous space, whence the supporting pedicle 

 of the hyoid, which ossifies and becomes the osselet styloide, arises. 

 The operculum, suboperculum, interoperculum, and preoper- 

 culum are not developed from the primitive cartilaginous arch, but 

 make their appearance as osseous deposits in the branchiostegal mem- 

 brane, behind, and on the outer side of, the posterior crus. 



If we turn to the higher Vertebrata, we find, as I have stated 

 above, that, at an early period of their embryonic existence, they also 

 present a cartilaginous arch, stretching from the ethmo-presphenoidal 

 cartilage to the auditory capsule, and supporting the mandibular or 

 Meckelian cartilage on the condyle furnished by its inverted crown. 

 The anterior part of the anterior crus of this arch becomes the pala- 

 tine bone, which is therefore truly the homologue of the fish's ^)aZ«- 

 tine. The posterior part of it becomes the pterygoid, which therefore 

 is the homologue of the pteryyoidien (and transverse !) of the fish. 

 The produced crown of the arch in the higher Vertebrata becomes 

 either the incus, or its equivalent, the quadratum. I therefore 

 entertain no doubt that the Jugal is really the homologue of the 

 quadratum of other oviparous Vertebrata. That the tympanal 

 has no relation whatsoever with the bone of the same name in the 

 higher Vertebrata is indubitable ; and I am unable to discover among 

 them any representative of it. It seems to me to be an essentially 

 piscine bone, to be regarded either as a dismemberment of the 

 quadratum or of the pterygoid. It may be termed the "meta- 

 pterygoid." 



Still less do I find among the higher Vertebrata in their adult 

 state, any representative of the posterior division of the suspensor. 



