MR. W. K. PARKER ON THE OSTEOLOGY OF BALANICEPS REX. 309 
they are mere flattened styles, just expanding at their distal extremities to send 
upwards and inwards a thin orbital plate; so that in these birds there is nothing 
startling in the idea of their being the ribs (pleurapophyses) of the nasal vertebra; nor 
would it be difficult, were we looking for cranial vertebra, to suppose that the small 
simple bones (the pterygoids) attached to them behind were their appendages. 
Pterygoid. (Pl. LXV. figs. 1 & 7 pg.) 
The pterygoid of the Balzniceps is nearly an inch long, flat in the middle, clubbed at 
both ends, carinate above, and thicker and more rounded below, especially at the distal 
end ; whilst the proximal end is marked with three ridges, one outside, one inside, and one 
beneath. The inside of the pterygoid, which is altogether the most concave, is scooped 
with three cavities, one in the middle, and one at each end; they communicate with 
pneumatic passages. The outer part of the proximal end has a slightly convex oblong 
condyle; the inner has three large and some smaller teeth, which it into the end of the 
paiatines. The distal end is obliquely scooped on its outside to form a shallow cup to 
articulate with the convexity of the os quadratum. Above this cup are some pneumatic 
holes, and above them a small spur, looking forwards. Synovial cartilage covers the 
oblong condyle at the proximal end, and lines the concavity at the distal, creeping on 
to the end of the bone. This small, oblong, thinnish, but really strong bone commu- 
nicates the motion of the quadratum to the palatines, as the zygoma does to the pre- 
maxillaries. Were the same bone in the Heron magnified twice its size, it would be 
scarcely distinguishable from that of the Baleniceps. The pterygoids are almost ossified 
by the eleventh day of incubation in the Chick, 
Os quadratum. (Pl. LXV. figs. 1, 3, 6 & 74q.) 
The os quadratum of the Baleniceps is a large, strong, quadrate bone, its upper 
side being 13 inch in extent, its posterior the same, its anterior 3 inch, and the in- 
ferior side, measured in a straight line across the condyles that fit into the lower jaw, 
1; inch. The large upper condyloid processes are 1 inch across; the outer appears 
externally, articulating with the squamosal, whilst the inner passes inwards and some- 
what backwards, and partly encroaches on the par- and ex-occipitals. These upper 
condyloid processes are not, like the lower, completely covered with articular cartilage ; 
for the cellular nature of the squamosal, petrosal, and occipital at this part allows 
them to touch the bone only at certain points, these more projecting parts being alone 
covered with articular cartilage: hence the discontinuity of that tissue on the head of 
the quadratum. The upper margin of the quadratum is sharp-edged and gently concave 
in outline ; it expands a little at the anterior end to form the crescentic tip of the orbital 
process, which is a quarter of an inch across at its enlarged end. ‘This orbital process 
VOL. 1V.—PART VII. FAIS 
