16 
‘ascending process’); the external naris between them terminates 
anteriorly in an acute angle. In palatal or dorsal view the snout 
appears extremely narrow from side to side, and there is a ‘waist’ 
between the anterior, dentigerous portion expanded horizontally 
into a ‘terminal rosette’ (Charig & Milner 1990) and the two rami, 
lower and upper, behind. 
The lower ramus is broken off transversely not far behind the 
anterior corner of each external naris, but its full extent on each side 
of the snout is demonstrated by clear indications of its overlap onto 
the laterodorsal surface of the left maxilla, indications which sug- 
gest that that too was tapered to a point. The dorsal surface of this 
ramus, forming the floor of the nasal cavity, slopes steeply down- 
ward on either side (i.e. it is merely a posterior extension of the side 
of the snout), but between these slopes is a deep sagittal V-shaped 
groove. 
The upper ramus tapers to a thin spike which presumably met the 
nasals; it has a smooth outer (i.e. dorsal) surface, but internally (i.e. 
ventrally), where it borders the nasal cavity, it bears on each side two 
longitudinal ridges, a low lateral ridge and a stronger medial ridge. 
Together these produce a shallow lateral groove on each side and a 
deeper median groove, in the bottom of which the latter suture 
between the paired premaxillae may still be traced intermittently. 
These ridges would somehow have supported the internasal septum 
and associated soft tissues, and the lateral grooves doubtless served 
for articulation with a forwardly projecting prong from the nasal on 
each side. 
In lateral view the ventral, dentigerous margin of the premaxilla is 
distinctly downturned, both anteriorly towards the tip and posteriorly 
towards the articulation for the maxilla; it is smoothly concave 
between. There is extensive pitting on the outside of the snout, 
especially towards the tip, which doubtless served for the exit of 
blood vessels and nerves; a row of nutritive foramina lies just above 
the bases of the teeth. 
In ventral view the terminal rosette has an elongated spatulate 
shape, around the edge of which lie six dental alveoli on the left side 
and seven on the right. In these thirteen alveoli only six teeth remain 
in place, four of them complete to the tip. The first four alveoli on 
each side are large; nos. 2 and 3 are the largest; nos. 5 to 7 decrease 
in size progressively. Interdental plates are present, each interrupted 
by a narrow gap which is rather more posterior than anterior in 
position. 
When the premaxilla is seen in palatal view, the area between the 
tooth rows on either side appears to be fully occupied by a pair of 
narrow, transversely rounded ‘elements’, sutured together in the 
midline and broken off short just behind the level of the last 
premaxillary tooth. Each tapers anteriorly to a combined point 
which abuts against the rear end of a median groove between the 
medial walls of the first alveolus on each side. Towards the rear each 
‘element’ expands ventrally. From the anterior apex a strongly 
interdigitating median suture between the two sides pursues a 
sinuous course backwards for some 30 mm; farther back the 
interdigitations cease and the two sides are separated by a narrow, 
elongated, median gap, on either side of which the ‘elements’ curve 
out laterally away from each other and then, more posteriorly, 
almost rejoin. In the region of the anterior half of the median gap 
their ventral surface is somewhat rugose, suggesting the possible 
presence in life of a horny pad in the roof of the mouth. 
These, however, are not separate elements (despite their close 
resemblance to vomers) but seem to be integral parts of the premax- 
illa; they form a pair of stout ridges that support the adjacent tooth 
rows, lying lateral to them. Posteriorly from the level of the 4" tooth 
they expand into two vertical flanges, roughly triangular in shape 
and extending ventrally to an apex just behind the level of the last 
A.J. CHARIG AND A.C. MILNER | 
(7") alveolus and then descending again to terminate just behind the 
subrostral notch. 
At the posterior end of the premaxillary tooth row, just below the 
anterior end of the ventral margin of the lower ramus, is a deep notch | 
which received a rectangular peg-like process on the anterior end of 
the maxilla. Just in front of this notch lies the subrostral foramen, | 
while just above the notch, in the outer surface of the premaxilla, lie 
three well-defined pits. A vertical bony buttress separates the notch | 
in front from the anterior end of the deep U-shaped trough behind. | 
VOMER (Fig. 2C). The ventral (i.e. palatal) surface of the con- 
joined two lower rami of the premaxilla bears what appears to be a! 
very deep median septum; this divides the concavity of the premax- | 
illary trough into a pair of broad, U-shaped, ventrally facing troughs. 
each of which received the dorsal edge of the front maxilla. We 
interpret this as the extreme anterior portion of the paired vomers, 
fused together to form an extremely slender, vertical lamina which’ 
lies in the midline and is clasped between the vertical flanges of the 
premaxilla (described above). It extends forwards as far as the level 
of the alveoli for the 4" premaxillary tooth on each side. The central 
part of this lamina is attached to the roof of the anterior part of the 
premaxillary trough (though the suture is partly obliterated); 
anteriorly and posteriorly there is a gap between the dorsal edge of | 
the lamina and the roof of the (inverted) trough. The extreme anterior 
end of the conjoined vomers tapers to a point and appears to project - 
downwards from the roof of the mouth, in the midline between the) 
premaxillae, an unlikely position that suggests postmortem dis- 
placement. 
| 
MAXILLA (Fig. 3). All that is preserved is the anterior part of the 
left maxilla, broken off through the 8" maxillary alveolus. Seen in 
lateral view, both its upper and lower margins are smooth curves, 
concave above, and with the lower (dentigerous) margin continuing 
without interruption around the anterior end; the two margins) 
approach each other posteriorly so that the whole element, though 
broad from top to bottom in front, narrows appreciably towards the 
posterior break. Just below the anterodorsal corner the rectangular’ | 
peg (referred to above under Premaxilla) projects forwards; the 
maxillary tooth row begins immediately below it and then curves! }; 
smoothly ina posteroventral direction; when premaxilla and maxillaj 
are placed together in natural articulation there is a small gap of] 
about 20 mm between the last premaxillary tooth and the first)» 
maxillary. In Dilophosaurus (Welles 1984) this gap in the tooth row 
is some 40 mm, in an animal which is only about two-thirds the size 
of the Baryonyx holotype. The maxilla extends anteriorly beneath) | 
the external naris but is separated from it by the ventral ramus of the! { 
premaxilla, so that its most anterior extremity lies some 45 mm ) 
farther forward than does the anterior corner of the external naris (in 
this it contrasts with the condition in Dilophosaurus, where there 1s 
very little overlap between the two elements and where the mos! | 
anterior point of the maxilla lies more or less beneath the middle ol} 
the naris). Just behind the rectangular peg the medial surface of thd = 
maxilla bears a shallow channel running in an anteroventral direc 
tion, forming the lateral margin of the external portion of thd » 
subrostral canal. 
Along the dorsal margin of the lateral face is the long, slightly » 
rugose articular surface for the lower ramus of the premaxilla; i) » 
tapers to a point 135 mm behind the front tip of the maxilla and 
little way below its dorsal margin. Behind and medial to this, the 
dorsal margin is smoothly rounded and forms the posterior part 0 
the ventral border of the external naris. The lower margin of the ». 
medial face of the maxilla is formed by a stout rounded ridge, lyin{| > 
immediately medial to the tooth row; running above this throughou| 
its length is the articulating surface for the palatine, the anterio} 
