ESPECIALLY MYCTOPHOIDS 75 
distinct transversely orientated oval fenestra is present at the hind end of the post- 
temporal fossa. This enters the neurocranium beneath the post-temporal fossa, and 
is bordered medially by parietal and epiotic and laterally by pterotic. The possible 
significance of this oval fenestra entering the cranial cavity is considered by Goody 
(1968 : 225). The pterotic crest bears a notch and a groove postero-laterally just in 
front of the hind end of the crest, the groove orientated postero-ventrally. The 
dilatator fossa, which housed the dilatator muscle of the operculum, is a vertically 
arranged facet produced by excavations of the sphenotic anteriorly and the pterotic 
posteriorly. The dilatator fossa is lateral in position and below it is the hyoman- 
dibular facet. This latter is an elongated facet consisting of a straight groove 
arising anteriorly on the sphenotic and being continued posteriorly on the pterotic. 
The pterotic therefore contacts the sphenotic anteriorly within the dilatator fossa 
and the hyomandibular facet. 
The sphenotic enters into the composition of the skull-roof and also forms the 
postero-dorsal corner of the orbit. Dorsally it projects laterally from beneath the 
frontal, and the surface is unornamented. The posterior surface of the lateral 
projection is excavated somewhat to produce the anterior end of the dilatator fossa. 
From the outermost region of the lateral extension a stout strut passes ventro- 
medially to meet a corresponding upward strut from the prootic. The anterior end 
of the hyomandibular facet is located behind this strut and below the dilatator fossa. 
In the orbit the sphenotic produces the major part of the hind wall, contacting the 
prootic ventrally, the pleurosphenoid medially and the frontal dorsally. The main 
infraorbital sensory canal crossed the dorsal surface of the sphenotic on which it 
appears to have connected with the otic branch of the infraorbital canal from the 
pterotic. 
The epiotic forms the postero-dorsal part of the cranial roof medial to the post- 
temporal fossa. The epiotics are separated in the mid-line by the supraoccipital and 
they contact the parietals anteriorly within the transverse groove already noticed. 
Postero-dorsally the epiotic is in the form of a raised rounded knob of bone which 
provided the articulatory surface for the dorsal limb of the post-temporal. On the 
posterior face of the skull the epiotic meets the supraoccipital and exoccipital 
medially and the intercalar ventrally. Within the extreme posterior end of the 
post-temporal fossa the epiotic contacts the parietal and pterotic where these three 
bones form the borders of the small oval fenestra entering the cranium below the 
post-temporal fossa. 
The supraorbital sensory canal ran in a tube of bone within the frontal, opening 
anteriorly on the edge of the frontal behind the mesethmoid region. Two sub- 
sidiary branches of the main supraorbital sensory canal arose from the main canal in 
the region of the centre of ossification. One branch passed antero-medially and 
opened on to the interorbital region of the roof ; the second passed postero-medially 
and opened on to the posterior surface of the frontal, from where it appears to have 
continued on the surface towards the parietal. The infraorbital sensory canal 
passed across the dorsal surface of the sphenotic within the groove present on that 
bone. It entered the lateral region of the frontal just posterior to the centre of 
