MR. W. K. PARKER ON THE OSTEOLOGY OF BALANICEPS REX. 283 
and a posterior expanded pair that form the anterior wall of the tympanic cavity and 
the superior and anterior boundary of the Eustachian tubes. The anterior or inner pair 
are represented in Balzniceps by two bevelled articular surfaces on the sides of the 
great rostrum near its middle. We shall give some tables showing the modifications 
of these parts in various birds relatively to the pterygo-palatine apparatus. In front 
of these facets the basi-sphenoid of Balzniceps becomes gradually thinner, ending in a 
quadrate wedge-like process two lines anterior to its proper preceding homologue, the 
descending plate of the pre-sphenoid ; to this plate the rostrum of the basi-sphenoid is 
anchylosed. Behind the articular facets the rostrum expands, at first gradually, form- 
ing a thick beam of bone three lines across, and then it suddenly expands on each side 
into the elegant, conchoidal, anteriorly incurved ecto-pterapophyses, the counterparts 
of the marginal wings of the basi-temporal. This element has most substance at the 
part where its tables and diploé pass into the descending plate of the orbito-sphenoids, 
just below the optic foramina. 
That this is a most important basi-cranial element in birds is seen from its connexion, 
which must be studied in immature specimens. In the Chick, on the eleventh day of 
incubation, more than the posterior third of the rostrum is ossified, and this ossific 
centre, convex below and scooped above to receive the cartilaginous plate of the pre- 
sphenoid, bifurcates behind, each posterior wing-like moiety lying just in front of, and 
above, the basi-temporals. This single mesial osseous centre appears to be identical with 
the distinct so-called pre-sphenoidal ossification spoken of by Dr. Kolliker (Berichte 
von der Kéniglichen Zool. Anstalt zu Wurzburg, 1849, p. 40) and Huxley (Croon. Lect. 
pert): 
In the Chick, on the fourteenth day, this ossification of the true basi-sphenoid has 
already occupied all but the tip of the rostrum, and posteriorly has grown upwards 
in the direction of the ali-sphenoids and petrosals, and backwards towards the basi- 
occipital. 
On the sixteenth day, however, these parts and their relations can be still more 
advantageously seen ; for by this time the anterior cartilaginous tip is very small, whilst 
the posterior end of this large and most elegant osseous centre has reached the basi- 
occipital on the mid-line of the cranial floor, about a line behind the sella turcica, thus 
entirely excluding the basi-temporals. The groove on the upper surface of the gradually 
widening rostrum is bounded behind by the anterior wall of the sella turcica with its 
middle and lateral ‘ clinoid processes,’ whilst opposite these processes the basi-sphenoid 
expands into the large ecto-pterapophyses, on the upper part of which the ali-sphenoids 
are attached ; nearly the anterior half mesially being occupied by the deep ‘ sella,’ the 
posterior margin of which is even and smooth, whilst its fundus is perforated by a large 
foramen (in adult birds) which communicates with the internal carotids. Behind the 
ecto-pterapophyses the basi-sphenoid contracts, its sigmoid converging margins articula- 
