302

272

bustus. With other smaller kinds of Moa, D rheides* exemplifies the less-mature age of
the larger kinds in the minor indications of muscular force. The paroccipital part of
the occipital surface bulges rather more abruptly outward and backward than in the
larger crania above described, leaving a correspondingly deeper depression between that
part (Pl. LXXV. figs. 2, 3, & 4, 4) and the superoccipital tract (ib. 3). The masto-paroc-
cipital wall of the tympanic chamber (ib. figs. 1 & 4, 4, 8) has a less angular, more arched,
border than in D. crassus. The basioccipital mammilloid tuberosities (Pl. LXXV. figs.2
& 4, 1' 1') are less prominent. The posterior walls of the Eustachian canals (fig. 4, c) in
one skull of Dinornis rheides are continuous, appearing to define the basioccipital from
the basisphenoid, with a median emargination ; but this is less marked in the two other
crania of the same species. All show, more or less strongly, the remnant of the basi-
sphenoidal mid vertical canal between the bases of the pterapophyses (5').

The alisphenoid (fig. 4, 6) swells out into an oblong tuberosity below the "oval
hole" ; a deep notch, with a small venous perforation, divides the swelling from the
pterapophyses (5'). The tuberosities are more prominent in Dinornis rheides than in
D. elephantopus or D. crassus 1; they correspond with the mesencephalic fossae, but are
pneumatic, and due exclusively to the outer table and subjacent diploe*.

The orbitosphenoids (ib. 10) are as unmistakably indicated (in birds) by their
essential characters as transmitters of the optic nerves, as are the alisphenoids by the
oval foramina ; no separate ossification of the descending orbital plate of the frontal
in a young Grouse, or Goose, or other bird could be mistaken for an orbitosphenoid
by any anatomist, save one constitutionally incompetent to appreciate or comprehend
the grounds upon which true homology is determinable. **

The presphenoid (fig. 4, 9) rostral in shape, as in all birds and most mammals, is of
great length, as in other Dinornithes and the Struthionidae generally ; it is compressed
behind its mid part, and again expands to a breadth equalling that of its hind part in
D. rheides : the under surface is subcarinate where compressed, transversely convex
where expanded ; it terminates as usual, in a point. At its base it is confluent, above,
with the orbito-sphenoids, and in advance of these with the prefrontals ; the line of
confluence with the latter extends outward in the form of a shelf, or transversely hori-
zontal plate, with an obtuse terminal angle on each side (9") ; on this plate rests the
olfactory hoop (cingulum olfactorium).

The prefrontals retail the character of those in the previously described species,
making no show (as they do in Struthionidae 3) upon the upper surface of the cranium.
The confluence of the nasals with the frontals, prefrontals, and lachrymals is very com-
plete ; the cleft between the nasals (fig. 3, 15) persists anteriorly.

Both nasals and frontals were unfortunately wanting in that instructive portion of
the cranium of the young Gigantic Dinornis figured in Pl. LIII. figs. 1, 2, 3. I have

1 They are still more prominent in D. gravis, to be afterwards described.
2 Pl. XXXI. fig. 1, 11 (Dromaius).