430 Ruyal Society .— 



constituted by the temporal and symplectique. 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 

 aiFording support to both the hyoid and mandibular arches, the hyo- 

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

 this division may well retain the name of symplectic. 



It is commonly supposed that the hyomaudibular, symplectic, 

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

 divisions of the quadratum of the higher Fertebrata. Such a view, 

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

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

 higher Vertehrata 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 al)ranchiate Vertehrata. 



If the pterygoid, transverse, and metapterygoid of the fish were 

 anchylosed into one bone, or if the corresponding region of the ])ri- 

 mitive cartilage were continuously ossified, the result would be a bone 

 perfectly similar to the pterygoid of the frog ; and I entertain no 

 doubt that the amphibian pterygoid does really represent these bones. 



The inferior ossification in the batrachian suspensorium certainly 

 answers to the quadratum, in Triton — whether it should be regarded 

 partly or wholly as a quadrato-jugale in the frog seems to be a ques- 

 tion of no great moment — inasmuch as we may be quite sure that 

 the lower end of the frog's suspensorium represents the quadrate or 

 incudal element in other Vertehrata. 



Thus it would seem, that in the manner in which the lower jaw is 

 connected with the cranium, Pisces and Amphibia, as in so many other 

 particulars, agree with one another, and differ from Reptilia and 

 Aves on the one hand as much as they do from Mammalia on the 

 other. And the difference consists mainly, as might be anticipated, 

 in the large development in the branchiate Vertehrata of a structure 

 which aborts in the abranchiate classes. A most interesting series of 

 modifications, all tending to approximate the ramus of the mandible 

 more closely to the skull*, is observable as we pass from the fish to 

 the mammal. In the first, the two are separated by the hyomau- 

 dibular, the quadrate, and the articular elements, the first of wliich 

 becomes shortened in the Amphibia. In the oviparous abranchiate 

 Vertehrata the cranium and the ramus are separated only by the 

 quadratum and the articulare, the hyomandibulare having disap- 

 peared. Finally, in the mammal, the quadratum and the articulare 

 are applied to new functions, and the ramus comes into direct contact 

 with the cranium. 



The operculum, subopercalum, and interoperculum appear to me 

 to be specially piscine structures, having no unquestionable repre- 

 sentatives in the higher Vertehrata. Much might be said in favour 



* Of course in a morphological sense, ^\^lether they are more or less distant 

 in actual space, is not the question. 



