88 OSTEOLOGY [Parr II. 
the apex of the inferior ala, to joi the interorbital septum, so as to form a bridge over the olfactory groove, 
behind that produced by the turbinated ala; the interval left between them, transmits a branch of the 
ophthalmic nerve with the accompanying vessels, which groove the outer surface of the turbinated ala, and 
escaping from between the nasal limbs are distributed to the nostrils. The outward expansion or development 
of the produced apex obliterates the fissure; the anterior wall of the orbit presenting only the olfactory 
outlet. 
There is thus left a space between the turbinated ala and the prefrontal, which is closed behind by the 
outward extension of the former; it lodges a part of the subocular pneumatic sinus, from which the pre- 
frontal receives air directly, by a large aperture on its inner surface. The compressed cavity internal to the 
turbinated ala is wider above and below, narrowest in the centre, where the olfactory orifice opens into it ; 
the apposition of the pituitary membrane with that of the pneumatic sinus beneath the lachrymal duct 
bounds it externally, and below it is continued over the groove on the inferior ala to open into the posterior 
nares by the concavity of the nasal process of the palatine bone. 
In Gowra, the prefronto-ethmoidal fissure is not obliterated. In Zreron, Geophaps, and Calenas, it is 
completely closed; in Curpophaga, Ptilinopus, and Didunculus, only partially so. 
In Zreron, Didunculus, and Calenas, &c., the turbinated ala is so curved outwards or evasated, as to 
come into contact with the apex of an inwardly inclined, subtriangular projection from the anterior margin 
of the prefrontal, supporting the termination of the lachrymal duct ; and thus the pneumatic space is divided 
into two compartments ; in Zreron, from the great expansion of the diploé, it is much reduced in size. 
In the Dodo, the prolongation of the interorbital septum, and the turbinated ale, project about five 
lines beyond the junction of the cranium and mandibular apparatus; completely concealed from above by 
the latter, but not in contact with it, as in other Pigeons. The resilient hinge having retrograded to the 
cranio-facial line, space is left to permit of the downward flexion of the mandible; the remainder of this 
mechanism we shall see hereafter. The curved plate is much widened out to lodge the olfactory apparatus, 
and the convexity comes in contact with the prefrontal, in its whole length, at that part of the inner surface 
of the latter, which corresponds to the lachrymal groove externally ; so that the subocular space is completely 
obliterated in the centre. The inferior ala is much compressed transversely and extended forward, so as to 
leave between it and the rostrum, a deep narrow groove; and the subocular space is reduced to a small 
irregular depression between its thin anterior edge and the prefrontal, with which it coalesces inferiorly. 
The prefronto-ethmoidal fissure is obliterated by the expansion of the posterior border of the turbinated 
ala, arching over the foramen that transmits the ophthalmic branch of the fifth nerve, which grooves 
the roof of the olfactory fossa. This aperture is diminished by an extension forwards of an osseous plate, 
from the interorbital septum outside of the foramen olfactorium ; it forms the outer part of the floor of the 
olfactory fossa, and is, as it were, an ossification of the external wall of the periosteal tube, which conducts 
the olfactory peduncle to its exit at the antorbital foramen in most other birds; here, the tube im relation to 
the extremely short olfactory peduncle is much abbreviated, and its base widened out, serving to obliterate 
the space intervening between the antorbital and olfactory foramina. The olfactory fossa has a subhemi- 
spherical base, perforated by the single aperture for the transmission of the olfactory nerve ; its floor presents 
the deep narrow groove just mentioned; the outer wall is perforated by the antorbital foramen about three 
lines anterior to the olfactory outlet. Each fossa is one inch two lines deep, and five lines wide at its 
anterior orifice; the height exclusive of the groove is six lines. The extremity of the high compressed 
rostrum is removed, exposing to view the very-loose diploé enclosed by thin and elastic parietes ; it pro- 
bably terminated in a subacute apex. The anterior thickened margin of the inter-olfactory septum is 
concave anteriorly, and its lower portion ascends obliquely backwards, to a deep notch immediately below its 
