474 PKOF. W. J. SOLLAS ON PLESIOSAURFS 



Fig. 10. — Oblique Fracture . through the SIcull of P. megacephalus, 

 showing the line of union of the maxilla and palatine. (Scale |.) 



n 



In, Internal nasal passage. 



praemaxillse, below by the vomers and palatines, and on each side by 

 the maxillse, and also in some parts of its course by the palatines. 



Fig. 11. — Transverse Fracture through the Skull o/P. megacephalus, 

 crossing the nasal chambers. (Scale |.) 



EN, external naris ; IN, internal naris. 



The vomers (fig. 11, Vo) form a trough-shaped bone of considerable 

 thickness, flat below but concave above, with a low ridge on each side 

 of the middle line ; its sides extend upwards, together with a process 

 from the palatines, as a curved wall for half the height of the central 

 chamber, which is thus divided through its lower half into a middle 

 and two lateral portions. The lateral portions have the appearance 

 of tubes sloping downwards and forwards. On each side of the 

 prseniaxillae the external nares open freely into the central chamber ; 

 while the foramina on each side of the vomers communicate with its 

 lateral passages. These passages are bounded externally by the 

 maxillae, and internally, as well as inferiorly, by the palatines. 



The oval foramina appear to represent the internal nares, since 

 they are similarly situated with respect to the surrounding bones as 

 the posterior nares of many Lacertilia ; and it is with this order that 

 Plesiosaurus stands in the closest connexion. 



