01 apteryx australis - University of Texas Libraries

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Of the bones more immediately concerned in the formation or motion of the jaws,
that element of the temporal may be first described which inbirds is always moveable
and articulated at once with the cranium and both the upper and lower jaws.
The tympanic bone is of a subcompressed trihedral form, and sends forwards into the
orbit a longer and slenderer process than in the larger Struthionidæ : its upper articular
surface is a transversely extended convex condyle, which plays ina corresponding
cavity internal to the base of the zygomatic process. The opposite extremity is expanded,
and presents two distinct articular convexities for the lower jaw, the inner one
being the largest : above the external convexity there is a small but deep depression for
the reception of the deflected extremity of the jugal bone.
The posterior extremity of the pterygoid bone is securely wedged inbetween the orbital
process of the tympanic and the transverse process of the sphenoid :as itadvances
forwards it expands, as in the other Struthionidæ , into a thin plate of bone, which is
bent upon itself with its concavity turned inwards, and is continued by anchylosis into
the palatine bones, so that the limits between them cannot be defined.
The palatine bones are inlike manner confluent withthe maxillaries. They are pierced
by two narrow elliptical posterior nasal foramina, about 3 lines in length, over which
the exterior margin of each palatine bone arches from without inwards, and these overarching
laminæ gradually approximate, as they advance forwards, and meet about one
inch anterior to the nasal foramina, from which an imperforate plate of bone, impressed
with a narrow median fissure, and composed of the confluent palatal processes of the
maxillary and intermaxillary bones, is continued to the end of the beak. The limits
between maxillary and intermaxillary bones are indicated by two fine oblique lines,
commencing at the outer margin of the roof of the mouth, about 2½ inches from the
apex of the beak.
The jugal style, which in the Ostrich may be separated in the full-grown bird into
a zygomatic and malar portion, consists in the Apteryx of a single slender compressed
twisted bone, anchylosed with the maxillary bone in front, and terminated behind
by an obtuse deflected extremity, which is received into a corresponding vertical
cavity in the upper part of the outer process of the tympanic bone. By this mode of
attachment the tympanic bone offers increased resistance to the pressure transferred to it
by the lower jaw, at the same time that itgives additional strength to the upper mandible.
It is continued backwards in the same line with the upper maxillary bone as in other
Struthionidæ, and is not bent downwards at its junction with the maxillary as in the
Ibis and other Grallæ.
The superior maxillary bone presents the singular form of a nearly perfectly flat
elongated triangular plate of bone, which is imperforate, and is continued by uninterrupted
ossification with the intermaxillary. The Rhea among the Struthionidæ
makes the nearest approach to the Apteryx in the structure of this part of the skull;
but the maxillary plate is perforated by large foramina, and sends upwards on each