210 MR. W. K. PARKER ON THE OSTEOLOGY 
It is originally developed as the ossification of an extension forwards of the cartilaginous 
pituitary floor, which extension becomes a grooved style underlying the true and more 
or less coalesced trabecule cranii. The bird comes nearest the Ophidians as to the size 
of this rostrum ; but in those creatures the basitemporals lie on nearly the same plane 
as the “ rostrum,” and intervene between it and the basioccipital. Nearly the posterior 
fourth of the rostrum is bare beneath; it is then for almost the rest of its extent 
sheathed by the overgrown vomer (PI. XL. fig. 1), just as originally it sheathed the lower 
edge of the ethmo-vomerine cartilage : with that it coalesces early,with the vomer not at 
all. Where the “‘ rostrum” is expanding behind into the thick portion of the basisphe- 
noid the skull-base expands on each side and forms the “ anterior pterygoid processes.” 
Behind the root of these is, on each side, the Eustachian opening, and behind and above 
these directly outstanding pedicles there are the ‘“‘ posterior pterygoid processes.” The 
former processes do not lean forward as in the Emu and Rhea, are not so long, and 
are much flatter ; they are depressed. Their development is altogether above and be- 
yond what is seen in any typical birds, and the nearest approach made to their con- 
dition is in the Syrrhaptes. The oval articular facet on the pterygoid, answering to 
the facet on the end of this transverse sphenoidal spur, has crept a little further for- 
wards than in the Rhea, which, again, is intermediate between the Tinamou and the 
Emu. 
All we have described hitherto is truly and essentially struthious. Still there is an 
advance, and the typical leaven has begun to work in the generalized Ostrich-form. 
The anterior clinoid processes are small prickles ; the posterior form one, continuous, 
strong wall of bone; the “ sella” is, as in the Ostriches, only moderately deep, as com- 
pared with that of typical birds; nor is it so neatly circular. The alisphenoid of the 
Tinamou (Pl. XL. fig. 3) is much like that of the Crocodile on the one hand, and of 
typical birds on the other. The external pterygoid process is a mere tubercle ; and, 
what is quite unusual and fish-like, the foramen ovale, at its infero-posterior angle, is 
divided into two by a bridge of bone. As in the Emu, Rhea, and Sparrow-Hawk 
(Accipiter nisus), the supero-posterior angle is developed separately into a “‘ postfrontal ” 
(Pl. XL. fig. 3, po.) homologous with that of the fish, because developed in cartilage, and 
only analogous with that of the Reptilia, which is a mere membrane-bone. Reptile- 
like, the suture between the alisphenoid and the orbital plate of the frontal is very long 
before it is obliterated, but it is also long separate from the anterior sphenoid (Pl. XL. 
fig. 3,p.s.). As each eyeball is about equal in bulk to the entire brain, the septum of 
the orbits is very large, and, as in birds generally, owes more to the ethmoid than to 
the anterior sphenoid. The upper edge of the alisphenoid is 6 lines in extent: the 
orbital ale are scarcely half a line across ; they must be looked for inside the skull ; 
and they retain their distinctness for a most unusual time—when the bird is quite 
adult. These small orbito-sphenoids are wedged between the orbital plates of the 
frontals and the supero-internal angle of the alisphenoid; between them is seen the 
