THE AXIAL SKELETON. 



563 



Tmx 



cartilage bones. Probably the slender rods known as quadrato-jugals 

 or jugals are also cartilage bones. 



Two parieto-frontals and two nasals above, a paired vomer and an 

 unpaired dagger-shaped parasphenoid beneath, and two lateral hammer- 

 shaped squamosals are membrane 

 bones. There is no basisphenoid 

 ossification. 



To these are added the small 

 premaxilla? in the very front of the 

 skull, and the long maxillae on each 

 side. The quadrato-jugal connects 

 the maxilla: 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, 

 consists of three pieces, --the 

 largest an articular angulo- 

 splenial, outside this a thin den- 

 tary, and anteriorly uniting with 

 its fellow a minute mentomecke- 

 Han. 



A delicate rod the columella 

 auris extends from the tympanum 

 to the fenestra ovalis in the internal 

 capsule of the ear. According to F iG. 273. Skull of frog-upper and 

 Parker, it represents the upper part lower surface. - After \Y. K. 

 of the hy oid arch, the lower portion Parker. 



Upper surface 



Pinx., premaxilla; N., nasal ; .I/., max- 

 illa; Sq., squamosal; (?./., quadrato- 

 jugal ; e.o., ex-occipitals ; P.f., parieto- 

 frontals ; Sph.E., sphenethmoid ; P.O., 

 pro-otic. 

 Lower surface 

 PIH.V., premaxilla 



of which forms the cartilaginous 

 or partially ossified hyoid plate, 

 which lies in the floor of the 

 mouth and is produced into two 

 anterior and two posterior cornua. 

 According to some others, the 

 columella is morphologically con- 

 nected with the ear-capsule. 



The teeth are borne by the pre- 

 maxilke, maxillae, and vomers. 



There is no parietal foramen, 



but in the Labyrinthodonts it is always distinct, and the pineal body is 

 supposed to have been well developed. The foramen is also very 

 distinct in some of the extinct "Ganoid"' Fishes. 



The cartilage which bears the quadrate at its lower end, and runs 

 between pterygoid and squamosal, connecting the articulation of the 



quadrato-jugal ; 

 pterygoid; Ps., 

 pro-otic; 



-I/., maxilla ; 

 Q., quadrate ; 

 parasphenoid ; 

 sphenethmoid 



r "_"- , <~tjr.j-*. t spiiciieujinuiu ; 

 palatine ; V., vomer ; c., columella. 



Q.J., 

 Pt., 

 P.O., 

 PL, 



