148 



MAEINE EEPTILES OP THE OXEOED CLAY. 



with which bone the maxilla has at most a very short union, being separated from it 

 to a large extent by the anterior end of the jugal. 



The nasals (n.) are very large elements which take a great share in the formation 

 of the upper surface of the rostrum. They meet in suture in the middle line, and 

 in the uncrushed condition were strongly convex from side to side (text-figs. 56, 57) ; 

 in some species (e. g. If. superciliosum) their posterior portion is considerably inflated. 

 Anteriorly they narrow to a point and are thrust between the maxilla? to a varying 

 degree, sometimes, as already noted, reaching the premaxillse. At their posterior end 

 they are separated from one another by the wedge-shaped end of the frontal, between 

 which and the prefrontals they send back a process of varying form and length. 

 Beneath the prefrontal they also send back a process, so that the anterior end of the 

 prefrontal is fixed in a deep bay or notch on their hinder end. The lower border of 

 the ventral prolongation unites below with the lachrymal in a straight suture. The 



Portion of skull in front of the orbit in Metriorliynchus (?) moreli : A, front wall of orbit ; 

 B, side of skull in front of orbit. (E. 3900, i nat. size.) 



for., lachrymal foramen ; /., jugal ; ?., lachrymal ; mx., maxilla ; n., nasal ; pr.f., prefrontal ; s.f., suture 

 for frontal ; s.pt., suture for union with palatine ; t, tubercle in groove in prefrontal. 



surface of the nasals is sculptured to a degree varying in the different species : usually 

 the sculpture in this region consists of longitudinal ridges which run into one another 

 irregularly. 



The prefrontal (pr.f.) is a large and solidly constructed bone which in nearly all 

 specimens is so crushed as to appear merely as a flat plate overhanging the orbit. 

 Actually it consists of two parts (text-fig. 57): (1) an upper portion which overhangs 

 the orbit and has its dorsal surface sculptured in most species, and (2) a downwardly 

 deflected region which helps to form the anterior wall of the orbit and bears a broad 

 groove running forwards on to the face from the orbit. The inner border of the upper 

 portion unites posteriorly with the frontal, anteriorly with the nasal ; its anterior end, 



