333

303

# 3. Pelvis of Aptornis otidiformis. ( Plate LXXXV. figs. 1-8;
Plate LXXXVI. figs. 1-4. )

My materials for the description of this instructive part of the skeleton are derived
from the small species (Apt. didiformis), and were obtained from Wanagnui, North
Island of New Zealand.

Referring for the definition of the bone called "sacrum" to my 'Anatomy of Verte-
brates,' "Aves," vol. ii. p. 29, I find it most convenient to adhere to the character of
"confluence of vertebrae in connexion with the pelvic arch." In the 'Archetype &c. of
the Vertebrate Skeleton' are discussed the characters by which the homologies of
the twenty "sacral vertebrae" of the Ostrich e.g. with the lumbar and caudal ver-
tebrae of Reptiles and Mammals may be determined ; therefore I need not be misunder-
stood if, to make plain, or easily comprehensible, the characteristics of the pelvis of the
extinct ground-birds of New Zealand, I continue to speak of such confluent series of
vertebrae as "sacrum".

In Aptornis the sacrum includes nineteen vertebrae (Pl. LXXXV. fig. 2, s 1-19). The
under surface of the confluent centrums shows well-defined modifications : it is pinched
into a median ridge in the first three; the ridge is then, as it were, scooped off, leaving
a smooth cncave surface or mid channel along the next six centrums, beginning and
ending in a point (fig. 2, c c'). From the hind point (c') a broadish obtuse ridge runs
along the next seven centrums, which gradually ose breadth. The seventeenth centrum
suddenly expands ; and those of the eighteenth and nineteenth have the form of broad
depressed plates moderately concave across ; the lateral confluent productions of the
vertebrae being defined by two pairs of small veritical canals.

The pleurapophyses of the first and second sacral vertebrae retain their moveabel
joints. The cup for the head of the rib (Pl. LXXXV. fig. 1, pl, pl) is oval, with the
small end upward, rather deep, well defined, and supported on an eminence at the upper
part of the centrum, nearer the fore end in the first than in the second sacral. The
surface for the "tubercle" is small, flat, cut obliquely at the fore part of the end of the
diapophysis, which expands above to contract bony union with its successor and with
the overlying ilium ((62). The unossified space left between the first and second sacral
diapophyses constitutes the foremost of the "interdiapophysial holes" (Pl. LXXXV.
fig. 2, i d'). The third pleurapophysis (ib. pl) is short, straight, expanded, and confluent
at both ends, broadest at that which underlies and is soldered to the ilium, beyond
which it does not extend. The fourth is still shorter, and abuts as a parapophysis
against the distal end of the third, with an extensive bony union above with the dia-
pophysis of its own verterbra. The fifth, sixth and seventh parapophyses lose length,
gain breadth, and abut, with complete confluence, against the ilium a few lines from its
lower margin ; the seventh blends with a smooth ridge-like thickening of the lower border
of the acetabulum as it passes to be continued into the origin of the ischium (63).

There then follow three sacrals without "parapophyses;" a side view of these, de-