Fig.7 Baryonyx walkeri, holotype, BMNH R9951; left postorbital. A, lateral view; B, medial. x 0.5. 
groove, running parallel to its posterior margin. From its posterodorsal 
region a large process projects mediad, like a flat-topped shelf 
supported strongly from below by a stout, rounded buttress; this 
presumably underlay the parietal. Anterior to this a weak concavity 
faces dorsomedially. 
FRONTAL, PARIETAL, AND ANTERIOR END OF BRAINCASE 
(LATEROSPHENOID, ORBITOSPHENOID) (Fig. 8). A stout plate of 
bone, very thick and with a smooth surface, and sheared off medially 
just to the right of the midline, comprises the greater part of the right 
frontal. It is continuous posteriorly with part of the parietal; a fairly 
straight line across the bone surface, more or less at right angles to 
the sagittal plane, may well be the suture between them. The parietal, 
behind that somewhat dubious suture, extends posteriorly and curves 
dorsally to form a steep transverse crest, thin from front to back; this 
crest, some 70 mm high, becomes thinner dorsally and ends in a flat 
top. The weakly concave ventral surface of the frontal is the ceiling 
of the posterior part of the orbit. The parietal and frontal together 
Fig.8 Baryonyx walkeri, holotype, BMNH R9951; right frontal and 
anterior end of braincase, in lateral view. x 0.5. 
A.J. CHARIG AND A.C. MILNER 
extend laterally to end in a large and extremely rugose facet for 
articulation with the postorbital; the parietal forms only the most 
posterior part of this facet, about one-sixth of its entire length. Along 
the anterior half of this facet the dorsal surface of the frontal (and 
presumably of the postorbital too) is raised into a conspicuous 
protuberance. Anteriorly, the frontal may have contacted the pre- 
frontal, but we cannot be sure of this. Ventrolateral to the frontal (and 
therefore ventral to the parietal) lies the laterosphenoid. 
The laterosphenoid forms the wall of the anterior part of the 
braincase, thick dorsally but tapering ventrally; in posterior view itis 
seen in section, behind which a gap separates its broken surface from 
the anterior face of the prootic (with which it once articulated). Its) 
shape, as preserved, is roughly tetrahedral. In lateral view it appears 
equilaterally triangular, with one apex directed forwards so that it just 
reaches the back end of the facet for the postorbital; dorsally it sutures 
with the parietal, and at its posteroventral corner its surface is) % 
extended outwards into a short shelf running more or less parallel}/ii 
with its lower margin. In ventral view it is again triangular, but this) 
time it forms a narrow isosceles triangle with the acute angle directed) m 
posteriorly; this surface is part of the internal wall of the orbit. They ii 
base of the triangle, at the anterior end, sutures with the frontal, and) i 
the anteromedial corner curves round medially to border a large) i 
notch which may have served for the emergence of cranial nerves II) 
(oculomotor) and IV (trochlear). Medial to this notch lies a thin.) 
eroded, subtriangular plate of bone, which, according to its general) ai 
shape and topographical relations, could well be the orbitosphenoid)} jp 
but it is too poorly preserved to be described properly. 
Ventral to the frontal and medial to the laterosphenoid (though ke: 
separated from the latter by a wide cavity) lies a confused mass olf & 
bone and matrix, the identity of which is not clear. As it is, quite) m 
fortuitously, almost symmetrical with the right-hand wall of the} jin 
braincase, it gives the impression that it might be the left-hand wall ie) 
preserved mostly as a natural mould in matrix: but it cannot bé i 
because it lies entirely to the right of the sagittal plane. 
POSTERIOR END OF BRAINCASE (WITH OTIC ELEMENTS) ANE Ws 
OCCIPUT (WITH BASISPHENOID) (Fig. 9). The supraoccipital, botl} j), 
prootics, opisthotics and exoccipitals (the latter two elements of the lefy 9, 
side detached as a separate fragment), and basisphenoid and basioc¢} p 
cipital are preserved. They are described from the posterior forwards} ». 
