METBIORHYNCHUS. 149 



as above described, being received into a deep bay in tbe hinder end of that bone. 

 The outer free edge overhangs the orbit and varies in form in the different species ; its 

 posterior border usually bears a number of small irregular notches, while its outer 

 border is thickened and passes down into the smooth ventral region. This latter 

 unites below with a process of the nasal in front and with the lachrymal behind. The 

 groove above mentioned as running from the orbit on to the face is partially blocked 

 at the edge of the orbit by a small pointed process (text-fig. 57, t.), the function of 

 which is not known. Behind this point the bone is curved sharply inwards to 

 form the upper part of the anterior wall of the orbit, the ventral part being joined 

 by the lachrymal. The ventral angle of the inner end of the prefrontal, together 

 with the lachrymal, is produced downwards into a short process terminating in a 

 sutural surface probably for union with the palatine (PI. XIII. fig. 2, pal.f.). 



The lachrymal {I.) is a solidly constructed bone which appears on the side of the 

 face in front of the orbit, of which it forms the antero-ventral portion of the border 

 and the lower part of the anterior wall (text-fig. 57). In front it unites with the 

 nasal above and the jugal below ; its anterior border bears a deep notch, at the bottom 

 of which is a small foramen (for.). From this notch the deep groove on the maxilla 

 runs forwards as described above, but it is not certain whether the maxilla has any 

 direct union with the lachrymal, though probably such a junction does exist for a short 

 distance at the hinder end of the groove. At the margin of the orbit the bone is 

 curved sharply inwards to form the front wall of that cavity. Above, it joins the 

 prefrontal, as above described, and its ventral inner angle is produced downwards with 

 that bone and helps to form the sutural surface for union with the palatine (PI. XIII. 

 fig. 2). Below, its straight ventral border joins the jugal in a broad sutural surface. 



The frontals (fr.) are represented by a single bone which never shows traces of a 

 median suture. It consists of a broad interorbital region with a median and a pair of 

 lateral posterior processes. The interorbital portion terminates anteriorly in a wedge- 

 shaped process thrust between the posterior ends of the nasals ; behind this it joins 

 the postero-internal border of the prefrontals, behind which again it forms the 

 posterior portion of the upper border of the orbit. The form and relations of the 

 nasals, frontals, and prefrontals to one another are of great importance in separating 

 the various species, as will be seen below. The lateral processes run outwards, down- 

 wards, and backwards, overlapping the anterior end of the postfrontals (po.f.) and 

 terminating in a point. The median process forms the anterior half of the ridge 

 between the temporal fossae, joining the parietal crest behind in a complex suture ; 

 the width of the upper surface of this median process differs in the different species, 

 and it may, or may not, bear sculpture. In the angle between the postorbital process 

 of the frontal and the median process a thin plate of bone, constituted by the lower 

 edge of the frontal and the posterior edge of the postfrontal, forms a floor to the 

 antero-internal portion of the supratemporal fossa (text-fig. 55). 



