5 62 



ON THE THEORY OF THE VERTEBRATE SKULL 



and more or less with the pterygoidien, which again are anteriorly 

 connected with the palatine. The flat tympanal is fitted in between 

 the pteiygoidien, jiigal, and temporal. 



Besides these numerous bones, there are four others which enter 

 less directly into the composition of the suspensorium. These are 

 the pre-opercule, a sort of splint-like bone which lies on the outer 

 and posterior faces of the temporal and jugal, and binds the two 

 together ; the opercide, which articulates with a special condyle 

 developed for it from the posterior edge of the temporal, above 

 the attachment of the hyoid ; the sousopercide, which lies in the 

 opercular membrane beneath this ; and lastly, the interoperciile, the 



Fig. 7. — Palatosuspensorial arch of Gasterosteus horn the inner side. HM. Hyomandibular 

 bone. Op. Its articular facet for the operculum. Po. Pre-operculum. H. Articular 

 surface for the styloid bone. Sy. Symplectic. F.Q. Palatoquadrate arch. Pa. Palatine 

 bone. Qu. Quadratum. Pt. Pterygoid. Mp. Metapterygoid. 



lowest of all, and commonly more or less closely connected with the 

 angle of the lower jaw. 



On examining the region in which these bones are eventually 

 found, in an embryonic fish, I discovered, in their place, a delicate 

 inverted cartilaginous arch, attached anteriorly, by a very slender 

 pedicle, to the angles of the ethmoidal cartilage, and posteriorly con- 

 nected by a much thicker crus with the anterior portion of that part 

 of the cranial wall which encloses the auditory organ (fig. 8). 



The crown of the inverted arch exhibits an articular condyle for 

 the cartilaginous rudiment of the mandible. The posterior crus is. 

 not, as it appears at first, a single continuous mass, but is composed 

 of two perfectly distinct pieces of cartilage applied together by their 

 edges. The anterior of these juxtaposed pieces is continuous below 



