ON THE THEORY OF THE VERTEBRATE SKULL 565 



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 

 " metapterygoid." 



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

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

 constituted by the temporal and symplectiqiie. It is quite clear, that 

 the temporal is not, as Cuvier's name would indicate, the homologue 

 of the squamosal. The whole course of its development would 

 negative such an idea, even if we had not a squamosal already ; 

 and I shall therefore henceforward term it, from its function of 

 affording support to both the hyoid and mandibular arches, the 

 hyomandibular bone, " os hyomandibulare," while the other bone of 

 this division may well retain the name of symplectic. 



It is commonly supposed that the hyomandibular, symplectic, 

 metapterygoid, and quadrate are all to be regarded as mere sub- 

 divisions of the quadratum of higher Vertebrata. Such a view, how- 

 ever, completely ignores and fails to explain, the connexion of the 

 hyoidean arch with the hyomandibular bone. In no one of the 

 higher Vertebrata does such a connexion ever obtain between any 

 part of the quadratum and the hyoid, which are quite distinct, and 

 attached separately to the walls of the cranium, in even young embryos 

 of the abranchiate Vertebrata. 



Nevertheless, in their very earliest conditions, these embryos are 

 said to present a structure, which, if I mistake not, shadows forth the 

 organization of the fish. The visceral arches, in which the man- 

 dibular and hyoid cartilages are developed, are at first separated to 

 the very base of the cranium by a deep cleft, the anterior visceral 

 cleft, so that the semi-cartilaginous rudiments of the mandibular 

 and hyoid are completely separate. Subsequently they are said to 

 coalesce above, as the visceral cleft diminishes, so as to have a 

 common root of attachment to the cranium ; and this, I apprehend, 

 answers to the hyomandibular bone, and its prolongation to the 

 symplectic. With advancing development, however, this part does 

 not advance, but remains stationary, and becomes confounded with 

 the wall of the cranium ; so that the two arches subsequently appear 

 to be attached to the latter quite independently, and there is nothing 

 left to represent this division of the Suspensorium in fishes. 



I am strengthened in this view by the structure and develop- 

 ment of the palatosuspensorial apparatus in the Amphibia, whose 

 consideration I deferred when speaking of the skull in that class. 



