568 ON THE THEORY OF THE VERTEBRATE SKULL 



quence of this is, that the articular surface for the hyoid appears 

 constantly to approach the cranial wall, until at length, in the adult,, 

 it seems to be almost in contact with it. If a knife were passed 

 obliquely between the pterygoid and the suspensorium, and then 

 carried through the suspensorium to its posterior margin a little- 

 above the condyle for the mandible, it would divide the suspensor 

 into a proximal and a distal portion, precisely resembling those which 

 naturally exist in the embryonic fish. If the proximal division 

 ossified, it would clearly represent the hyomandibular and symplectic 

 bones. Now in the Ampliibia, although the suspensor is not thus- 

 divided, it ossifies very nearly as if it were, and the superior or 

 proximal ossification is the so-called " temporo-tympanic,'' " temporo- 

 mastoid," or " squamosal " bone.'^ 



That this bone is really the homologue of the hyomandibular and 

 symplectic in the fish, becomes, I think, still more clear when we 

 compare it with such an aberrant form of piscine suspensorium as 

 is presented by some of the eel-tribe {Murcsna, e.g.). In these fishes. 

 the suspensorium is formed by only two bones, a small distal quad- 

 ratum, which, as usual, articulates with the lower jaw, and a large 

 wide proximal bone, which articulates above with the post-frontal and 

 squamosal, gives attachment to the operculum and to the cornu of the 

 hyoid, and sends down a process towards the articular head of the 

 quadratum. The single bone, which represents the three pterygoids, 

 of other fishes, is articulated for the most part with the quadratum,, 

 but partly with this proximal bone. The latter, therefore, clearly 

 represents both the hyomandibular and the symplectic bone's of 

 ordinary fishes. 



But if the suspensorium of Triton be compared with that of 

 Murcena, e.g., it will, I think, be hardly doubted, that while the 

 distal ossification in the former corresponds with the quadratum, 

 the proximal answers (at any rate, chiefly) to the hyomandibular 

 hox\^ o{ \!i\Q MiircBna. Indeed it differs from the latter principally in 

 being an ossific deposit in the outer portion only of the primitive 

 cartilage.- 



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



^ See this result, -well worked out, by the method of gradation only, by Kostlin (/. t. pp. 

 328-332), who draws particular attention to the resemblance between the suspensorium of 

 the Amphibia and that of fishes of the Eel-tribe. 



^ In Mill-ana Helena the suspensorium forms an obtuse angle with the axis of the skull, 

 though not so obtuse as in the frog. A strong ligament connects the outer side of the distal 

 end of the quadratum with the maxillary bone, passing outside the lower jaw. If the posterior 

 end of the ligament were ossified, it would correspond very nearly with the " quadratojugal "' 

 of the frog. 



