tO 
tN 
Fig.9 Baryonyx walkeri, holotype, BMNH R9951; occiput and posterior part of braincase, lacking detached left opisthotic. A, posterior view; B, right 
lateral. x 0.5. 
lateral processes of the prootics. In the midline of the anterior 
surface is an extremely prominent, ridge-like septum which divides 
ventrally (like an inverted Y ) into a pair of ridges, each leading down 
towards the basipterygoid process of its side; between the two ridges 
is a deep cavity. On either side the flat surface of the basisphenoid 
slopes posterolaterally so that the whole resembles a pitched roof. At 
the dorsomedial corner of each flat surface, just beneath the postero- 
lateral process of the prootic, is a moderately deep hollow. 
JUGAL (Fig. 10). The left jugal is represented by an elongate 
portion from the centre of the element, lacking what was probably a 
significant length at either end. In lateral view the lower margin 
appears almost straight, while the upper margin forms a smooth, 
shallow, concave curve that is the wide ventral border of the orbit; 
thus the element is beginning to widen towards the break at either 
end, the posterior widening being much the larger of the two. The 
lower margin is generally rounded, the upper margin sharper. The 
central part of the bone, directly beneath the centre of the orbit, is 
fairly robust; the ends of the fragment, however, become rapidly 
thinner towards the breaks (forwards, backwards and upwards). 
The lateral surface is more or less smooth except for a weak ridge 
running diagonally across the suborbital bar, from the upper margin 
of the bar beneath the front of the orbit to the lower margin of the bar 
at about the level of the back of the orbit. 
The medial surface, by contrast, is distinguished by a series of 
features. The lower margin is wrapped around to form a strong, 
A.J. CHARIG AND A.C. MILNER | 
dorsomedially directed flange; this flange is especially well devel- 
oped beneath the ascending process, and it passes anteriorly and a} 
little ventrally, becoming weaker as it does so, to merge into the) 
lower margin itself beneath the orbit. Beneath the orbit, too, it is) 
flattened, ridged and grooved parallel to its own length to form an 
articulation that presumably met the ectopterygoid. Posterior to this, 
where the flange is developed much mote strongly, it encloses a deep} 
trough between the main body of the jugal and itself. 
border of the deep trough enclosed by the ventral flange, the troug 1 
being at its narrowest at this point. The flange, and therefore the) 
trough which it helps to enclose, taper away to disappear entirely just) )_ 
directed process of the quadratojugal. 
The missing anterodorsal corner of the jugal presumably articu- 
lated with the maxilla and the posterodorsal corner with the). 
postorbital. 
QUADRATE (Fig. 11). Both quadrates are preserved complete, each 
with a broad transverse articulation for the lower jaw at its ventral) 
