THE ANATOMY OF BIRDS. — OSTEOLOGY. 159 
thickened by the underflooring of the parasphenoid (fig. 70, rbs). The rostrum often bears 
on each side a basipterygoid process (ap),— a smooth facet with which the pterygoid artic- 
ulates. These processes may be very 
strong, and far back on the basisphenoid 
body, when the pterygoids articulate with 
them near their own posterior ends, as 
in the struthious birds and tinamous (fig. 
75, btp); or they may be further along 
ou the rostrum, and the pterygoids then 
articulate near or at their fore-ends. The 
rostrum may be produced far forward, 
beyond the maxillo-palatines and vomer 
even, as in an ostrich; or it may bear the 
vomer at its end: or may be embraced 
by forks of the vomer ; the palatines may 
glide along it, or be remote from it on 
either side. In any event, whatever its 
production, whatever part may be eth- 
moidal, or basisphenoidal, or parasphe- 
noidal thickening, pterygo-faceting, ete., 
this ‘‘beak™ of the basisphenoid is 
always in the axis of the base of the 
skull, and at the bottom of the inter- 
orbital plate: it may be horizontal, or 
obliquely ascending forward; and the 
variety of its relations with the pterygo- 
palatine and vomerine mechanism fur- 
nishes important zodlogical characters, 
as we shall see when we come to treat 
of palatal structure particularly. Just at 
-the base of the beak, where it widens 
into the main body of the bone, may 
commonly be seen, coming from between 
the sphenoidal body and the lip of the 
basitemnporal underflooring, the orifices 
of the eustachian tubes. and often also 
the anterior ends of the carotid canal. 
If a bristle, passed into a questionable 
Fic. 71.— Ripe chick’s skull, in profile, x 8 diameters; after 
Parker. pr, premaxillary; ain, ali-nasal cartilage; en, septo- 
nasal; 7, nasal bone; 7, lacrymal; pe, perpendicular plate of 
ethmoid, as in fig. 70; ps, presphenoidal region; as. alisphe- 
noid; 7, frontal; p, parietal; sq, squamosal; so, superoccipital ; 
eo, exoccipital; oc, occipital condyle; st, the cross-like object, 
the stapes, whose foot fits fenestra ovalis, see fig. 83; g, quad~ 
rate; pg, pterygoid; ¢j, quadratojugal; j, jugal; pa, palatine; 
mz, maxillary. In the mandible: d, dentary; su, surangular; 
a, angular; ar, articular; iap, internal angular process: pap, 
posterior angular process. 2, optic foramen; 5. foramen ovale, 
foramen here, comes out of the ear, it for inferior divisions of the 5th nerve. (Compare fig. 70.) 
has gone through the eustachian tube: if it comes out below the ear, on the floor of the skull, 
outside, it has run in the carotid canal. The extent of the alisphenoids (figs. 70. 71, as) can- 
not be determined in old skulls. They lie at the back lower border of the orbital cavity, clos- 
ing in most of the brain box that is not foreclosed by the frontal bone. You will alcays find 
at the back of the orbit. close to the mid-line, and rather low down, the very large optic fora- 
mina (any figs., 2); alisphenoid should not extend in front of these orifices. A little below and 
behind the optic foramina, and much more laterally, not far from the quadrate itself, is a con- 
siderable foramen, quite constant, fur transmission of the inferior divisions of the fifth (trigeminal 
or trifacial) nerve. This is the foramen ovale (any figs.. 5): it is either in the alisphenoid, or 
between that bone and the prodtic; it must not be mistaken for one of the several smaller holes. 
usually seen close about the optic foramen, which transmit the nerves (oculo-motor, pathetic. 
