THE KEPTILIAN CLASS OF THE MOSASAURID^. 



689 



near the coronal suture ; but in Amblyrhynchus and other Igua- 

 nians this foramen is in that suture. 



Tig. 7. 



Fig. 8. 



Monitor niloticus. 



Upper surface of cranium. 



Python. 



In the Python, fig. 8, and all other Ophidia, the temporal fossae, 

 t y have no outer boundary, there being no zygomatic arch : the 

 " diverging appendages " of the maxillary, viz. the malar and squa- 

 mosal bones, are suppressed. The parietal is feebly notched behind, 

 not bifurcate. The mastoid, 8, overlaps the alisphenoido-parietal 

 suture by a squamous articulation, projects far behind the occipital 

 surface of the skull, and there supports the tympanic column by an 

 oblique terminal flat articular facet (s', and fig. 4, s'). The parietal, 

 7, as in the Crocodilia, is imperforate. 



In Mosasaurus Hoffrnanni (fig. 6) there is a large foramen parie- 

 late (7 *), which, as in the Monitor, is wholly in the parietal, 7. The 

 parietal bifurcates posteriorly ; its prongs, 7', extend backward and 

 outward, and articulate with the mastoid, 8 ; and this bone curves out- 

 ward and downward to join the squamosal, 27, and, with it, to form 

 the articular surface for the tympanic. Anteriorly the squamosal 

 unites with the postfrontal, 12. The long and wide temporal 

 fossae are thus bounded, externally, as in Lacertians, by a long and 

 narrow zygomatic bridge, in the composition and proportions of 

 which the Mosasaur most resembles the Monitors and Iguanas. 



