XIII 



PHYLUM CHORDATA 



341 



and the same holds good of v the parietals. Both palatine (PI) 

 and pterygoid (Pt), as well as maxillae, develop palatine plates 

 in the roof of the mouth, cutting off a nasal passage of great length 

 from the cavity of the mouth, the posterior nares (ch) being situated 

 far back towards the posterior end of the cranial base. The nature 



FIG. 1003. Ventral view of the skull of Chelone mydas. bs. basi-sphenoid ; fr. frontal ; 

 j. jugal ; m. maxilla ; ob. basi-occipital ; ol. exoccipital ; op. opisthotic ; os. supra-occipital ; 

 pal. palatine ; par. parietal ; ph, post-frontal ; prfr. pre-frontal ; pt. pterygoid ; prm. pre- 

 maxilla ; q. quadrate ; qj. quadrato-jugal ; sq. squamosal ; v. voraer. (After Hoffmann.) 



of the articulation between the mandible and the quadrate is 

 such that movement is restricted to the vertical plane, and lateral 

 displacement is further provided against by the development of 

 a broad process of the pterygoid against which the inner surface 

 of the mandibular ramus plays, an arrangement which occurs also 

 in most Lacertilia. 

 VOL. IT Y 



