278 MR. W. K. PARKER ON THE OSTEOLOGY OF BALANICEPS REX. 
day after hatching, these three pairs of osseous centres are about equal to what may be 
seen in the Chick on the eleventh day (nine days before hatching). 
Looking at the side of the Baleniceps’ skull between the post-frontal and squamosal, 
there may be seen, eight lines mesiad of the anterior spur of the latter, a large oval 
foramen, which has a conjugational relation between the petrosal, ali-sphenoid, and 
basi-sphenoid. This passage (the foramen ovale) transmits the chief part of the tri- 
geminal nerve, and is one of the best landmarks in the study of the anatomy of the 
cranium in all the Vertebrata. This aperture is wide below and narrow above ; it is four 
lines in extent in its long diameter, the direction of which is backwards and outwards. 
A bristle passed across the floor of the cranium through both the foramina ovalia lies 
one line behind the posterior clinoid processes. 
Ali-sphenoids. (Pl. LXV. fig. 1, as.) 
The ali-sphenoid of Baleniceps is crossed at its upper third by an ascending crescentic 
ridge which joins the post-frontal process and forms the antero-inferior boundary of the 
temporal fossa. At one-eighth of an inch in front of the foramen ovale there is a tri- 
angular eminence in a line with the middle of that passage; and at the same distance 
in front of this eminence, but higher up, a twin passage exists. This divided passage 
is a little below and behind the great optic foramen, which opens freely into its fellow of 
the opposite side, and which notches the posterior border of the connate orbito-sphenoid. 
The optic foramen of Balzniceps is half an inch in front of the foramen ovale and one- 
third of an inch higher up. A bristle passed through both the optic foramina lies in front 
of the anterior margin of the very deep sella turcica, and passes across the middle of 
the anterior or, rather, internal margin of the ali-sphenoids. The optic foramen is four 
lines in diameter; its shape is ovoid, the narrow end pointing outwards and a little 
downwards. Half an inch above this foramen another exists, half its size; this is the 
remains of that membranous tract in the primordial cranium between the cartilaginous 
interorbital septum and the cartilage in which the ali-sphenoid was developed: through 
a passage in the lowest part of this tract the optic nerve passed. By means of the 
extension of ossific matter from the growing ali-sphenoid, and the diverging alz of the 
orbito-sphenoid, this membranous tract becomes bony for more than its middle half, its 
upper part continuing membranous, and its lower third becoming the large well-mar- 
gined optic foramen. 
There is a considerable eminence on the ali-sphenoid, two lines above the foramen 
ovale, which breaks into two elegant crescentic ridges, the anterior ridge passing at the 
distance of a line behind the one already described to the base of the post-frontal, whilst 
the posterior ridge passes outwards and backwards to the quadrato-squamosal joint. 
The bone across this middle part is very thick and cellular. 
