326 



ZOOLOGY 



SECT. XIII 



orbital septum (Fig. 935, Si). The posterior part of the skull has ? 

 in the Turtles (Fig. 936, A), a false roof formed by upgrowths of the 

 occipital, parietal, and squamosal. The palatines (pal) are approxi- 

 mated, and develop palatine plates which for a short distance cut off 

 a nasal passage from the cavity of the mouth. The rami of the 

 mandibles are stout, and are firmly united together at the symphysis. 

 In the Crocodiles (Fig. 937), as in the Chelonia, the quadrate 

 (Qu) is firmly united with the other bones of the skull. There is a 



Prl 



Ptf ??* 



Pmx 



FIG. 934. Skull of Hatteria, viewed from the side (upper figure) ; from below (lower left-hand 

 figure) ; from above (lower right-hand figure) ; and from behind (central figure). A , orbits ; 

 ang. angular; art. articular ; Bo. basi-oecipital ; C'h, internal nares ; d. dentary ; Exo. ex- 

 occipital ; Fr. frontal ; Ju. jugal ; mx. maxilla ; N. external nares ; Na. nasal ; Op. o. opisthotic ; 

 Pa. parietal ; P. mx. pre-maxilla ; P. or Post-orbital ; Prf. pre-frontal ; Pt. f. post-frontal : 

 (Jit. quadrate ; Qr. J. quadrate -jugal ; So. supra-occipital; &p/i, basi-sphenoid ; Sq. squamosal: 

 Vo. vomer. (After Zittel.) 



membranous and cartilaginous inter-orbital septum. Both palatine 

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

 in the roof 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 

 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 



