THE AXIAL SKELETON. 



583 



Tmx 



and an unpaired sphenethmoid forming the front of the brain-case, are 

 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 (para- 

 quadrates) are membrane bones. 

 There is no basisphenoid ossifica- 

 tion. 



To these are added the small 

 premaxillce in the very front of the 

 skull, and the long maxillae on each 

 side. The quadrato-jugal connects 

 the maxillae 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. 

 , 'Tach'~rTalf 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 FlG. 314. Skull of frog upper 

 to Parker, it represents the upper and lower surface. After W. K. 

 part of the hyoid arch, the lower Parker, 

 portion of which forms the car- Upper surface 



tilaginous or partially ossified Pmx., premaxilla ; N., nasal ; M., max- 

 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- 

 maxillse, maxillse, and vomers. 



There is no parietal foramen, 

 but in the Labyrinthodonts it is 



Qj. 



., nasai , 



squamosal ; (X/., < 

 ->ccipitals ; P./ 



'., sphenethmoid ; P.O., 



ilia; Sy.j squamosal; Q.j.-, quadrato- 

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



frontals ; J 



pro-otic. 



T.ower surface 



Pmx.) premaxilla; M. t maxilla; Q.J., 

 quadrato-jugal ; <?., quadrate ; Pt. t 

 pterygoid ; Ps., parasphenoid ; P.O., 

 pro-otic ; Sp.E.^ sphenethmoid ; PI., 

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



always distinct. 



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- 



