98 OSTEOLOGY [Parr II. 
mandibular beam which here is chiefly constituted by the ento-nasal limbs, exists at the anterior edge of 
these plates, and in front of the posterior extremity of the nasal fissure. In the Dodo, on the contrary, 
this hinge is in the same transverse line as the hinder angle of the fissure, and the mesial beam is, as it were, 
started off the flat arch, formed by the turbinated al, which projects free under the mesial beam, separated 
from it by a space permitting the downward flexion of the mandible; the flexibility of the upper beam 
being increased by the thinning away of the part which conceals the free portion of the turbinated ale. 
The bifid posterior extremity of the mesial process of the premaxillary is much smaller than in the Dodo, it 
passes beneath the coalesced nasals, resting on the upper edge of the inter-olfactory septum, and reaching 
about half-way to the frontal border of the nasal; in the Dodo, this extremity is much broader, and forms 
the principal part of the mesial beam at the hinge; and it reaches further back, separating the nasals 
mesially ; its apex corresponding to the anterior extremity of the coronal suture. (See Plate X., Fig. 4 4). 
In Treron, the diploé of the anterior portion of the coalesced frontals, is more expanded than 
in Gowra, and the frontal aspect is convex transversely, and in the antero-posterior diameter; while in 
Goura it is concave transversely, and depressed longitudinally; the increased pneumaticity invades the 
nasals and overflows the extremity of the mesial beam, forming a tumid and abrupt cranio-facial line. The 
compact elastic extremity of the premaxillary process is wedged between this expansion and the 
inter-olfactory septum. ‘The frontal aspect is depressed for a crescentic space, on each side, internal to the 
superciliary margin, and raised in the centre. (Jd. Fig. 3 4.) 
In Didunculus, the forehead is flatter longitudinally than in Zreron, but the broad extremity of the 
mesial mandibular beam is, in like mamner, overhung by the tumid convex segment of the expanded and 
coalesced nasals ; the central elevation of the frontal region is broader. (4, Fig. 1 4). 
In all the lesser Pigeons, the arrangement of the mandibular hinge is essentially as in Gowra; in 
Goura, Geophaps, and other slender-billed Pigeons, the ento-nasal limbs are very narrow posteriorly, hence 
the hinder angles of the nasal fissures are widened out, and expose to view the turbinated ale, In Ca- 
Jenas, the mesial beam is broader at the hinge, owing chiefly to the greater width of the nasal process of the 
premaxillary ; and the posterior angles of the nasal fissures are reduced to narrow chinks, asin the Dodo; in 
Treron and. Didunculus, these angles are also obliterated ; but in all, the extremity of the nasal process of 
the premaxillary is concealed mesially by the junctién of the nasals, and does not ascend on the frontal 
region to separate the nasal bones from each other, as in the Dodo, 
The lateral aspect of the cranium in the lesser Pigeons differs from that in the Dodo, in the large 
relative size of the orbit, and in the great ratio which it bears to the temporal segment of the orbito-tem- 
poral fossa; the latter bemg diminished by the bending down of the mastoid clement. The interorbital 
septum intervenes between the cerebral and olfactory fossee: its junction with the coalesced frontals is 
traversed by the olfactory groove, which terminates in the antorbital foramen; the septum is thick and 
complete in Zreron, in most other Pigeons it is thinner, and perforate in front of the common anterior 
boundary of the optic outlets: the floor of the cerebral cavity also is frequently membranous behind the 
olfactory foramen. In Geophaps, the post-orbital process is elongated, and nearly meets the post-temporal 
process of the mastoid; in Didwnculus, the strong post-temporal plate is extended forwards and joins a 
slender bar from the post-orbital process, which completes externally the circular temporal outlet. 
Inferiorly, the rostrum of the sphenoid in the lesser Pigeons is necessarily more elongated than in the 
Dodo; the pterygoid articular surfaces do not exist in the Didunculus; even in Gowra, they are much 
reduced in size; in Geophaps and Goura, the groove on the rostrum leading from the common outlet of the 
Bustachian tubes is well marked, and the lateral venous depressions are also perceptible in Gouwra; the 
existence of these markings depending on the pneumatic expansion of the rostrum. The sphenoid and 
prefrontals are much inflated in Zreron and Geophaps. 
