654 



PHYLUM CHORDATA : CLASS AMPHIBIA 



Tmx 



is finally represented only by the vestiges in the centra of 



the vertebrae. 



The skull consists — {a) of the persistent parts of the 



original cartilaginous brain- 

 box or chondrocranium, de- 

 veloped, as in the skate, 

 from parachordals and tra- 

 beculae, plus nasal and 

 auditory capsules ; {b) of 

 ossifications of parts of the 

 chondrocranium, cartilage 

 bones ; ic) of membrane or 

 investing bones ; and {d) of 

 associated visceral arches. 



Two ex-occipitals bounding the 

 foramen magnum and forming 

 the condyles, two pro-otics or 

 ossifications of the original audi- 

 tory capsule, 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 squamo- 

 sals (paraquadrates) are mem- 

 brane bones. There is no basi- 

 sphenoid ossification. 



To these are added the small 

 premaxilL-e in the very front of 

 the skull, and the long maxilla) 

 on each side. The quadrato- 

 jugal connects the maxillae with a 

 minute nodule which represents 

 the quadrate bone. 



On the roof of the mouth, 



extending 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, leased on Meckel's cartilage, consists of 

 three pieces — the largest an articular angulo-splenial, outside this a thin 

 dentary, and anteriorly uniting with its fellow a minute mentomeckelian. 



Fig. 375. — Skull of 

 and lower surface. - 

 Parker. 



frog— upper 

 -After W. K. 



Upper surface — 



Pmx., Premaxilla ; N., nasal ; M., max- 

 •illa ; Sq., squamosal ; Q.j., quadrato- 

 jugal ; CO., ex-occipitals ; P.f., parieto- 

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

 pro-otic. 



Lower surface — 

 Pmx., Premaxilla ; A/., maxilla ; Q.j., 

 quadrato-jugal ; Q., quadrate ; Pt., 

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

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

 palatine ; v., vomer ; c, columella. 



