THE AXIAL SKELETON. 
583. 
and an unpaired sphenethmoid forming the front of the brain-case, are 
cartilage bones. 
or jugals are also cartilage bones. 
Probably the slendet rods known as quadrato-jugals: 
Two parieto-frontals and two nasals above, a paired vomer and an 
unpaired dagger-shaped parasphenoid beneath, and two. lateral 
hammer-shaped squamosals (para- 
quadrates) are membrane bones. 
There is no basisphenoid ossifica- 
tion. 
To these are added the small 
premaxillze in the very front of the 
skull, and the long maxillze on each 
side. The quadrato-jugal connects 
the maxille with a minute nodule 
which represents the quadrate 
bone. 
On the roof of the mouth, ex- 
tending from the quadrate forwards 
to near the vomers, are the 
triradiate pterygoids, while at 
right angles to the anterior end 
of the parasphenoid’ and behind 
the vomers are the palatines. 
Each half of the lower jaw, 
based on Meckel’s cartilage, con- 
sists of three pieces,—the largest 
an articular angulo-splenial, out- 
side this a thin dentary, and 
anteriorly uniting with its fellow 
a minute mentomeckelian. 
A delicate rod—the columella 
auris— extends from the tympanum 
to the fenestra ovalis in the inter- 
nal capsule of the ear. According 
to Parker, it represents the upper 
part of the hyoid arch, the lower 
portion of which forms the car- 
tilaginous ‘or partially ossified 
hyoid plate, which lies in the floor 
of the mouth and is produced into 
two anterior and two posterior 
cornua. 
The teeth are borne by the pre- 
maxillze, maxillee, and vomers. 
There is no parietal foramen, 
but in the Labyrinthodonts it is 
always distinct. 
Fic. 314.—Skull of frog—upper 
and lower surface.—After W. K. 
Parker. 
Upper surface— 
Puix., premaxilla ; 1V., nasal; J7., max- 
illa; Sy., squamosal; Q.j., quadrato- 
jugal ; ¢.0., ex-occipitals ; PA, parieto- 
frontals ; S#2.Z., sphenethmoid ; P.O., 
pro-otic, 
Lower surface— 
Pmzx., premaxilla; JZ, maxilla; Q.7., 
quadrato-jugal; @., quadite Pt, 
pterygoid; Ps., parasphenoid; P.O., 
pro-otic; SJ.Z., sphenethmoid; Pd, 
palatine ; ., voiner ; ¢., columella. 
The cartilage which bears the quadrate at its lower end, and runs 
between pterygoid and squamosal, connecting the articulation of the 
lower jaw with the side of the skull at the auditory capsule, is called 
the suspensorium, 
In Elasmobranchs the hyomandibular is the sus- 
