374

344

On a first view of the pelvic viscera, as exposed by removal of the intestines, the kidneys
appear to be chiefly developed anteriorly, the broad lobes there extending beyond the
ilia with a convex border covering, or lying in contact with, part of the iliac origins of
the abdominal muscles. The length of these anterior renal lobes equals that of the
antacetabular part of the pelvis in Aptornis defossor; the second lobes, commencing
mesiad of the anterior ones, acquire their greatest breadth where those terminate, but
are here much narrower than the anterior lobes. Thence the middle lobes contract
where the ischia join the sacrum, and to blend with each other ; but it is merely
close contact, they are distinct¹.

On each side of the hind part of the kidney is the belly of the "obturator internus" or
postrenal muscle, which underlies the inferior opening of the ilio-ischial excavation.

This muscle being removed, the renal substance is found to pass "neurad," expanding
to a breadth equal or superior to that of the anterior lobes, with much greater depth
or thickness in the neuro-hæmal or dorso-ventral direction; and this the true posterior
renal lobe is shown, by a vertical longitudinal section of the side of the pelvis, to fill the
whole of the great posterior ilio-ischial cavity, extending from the partition bounding
posteriorly the interacetabular cavity backward to above and beyond the ischio-iliac
deck-like plates (Pl. LXXXVIII. fig. 2, v).

The vertebræ numbered ^{19, 20} in P1. LXXXVIII. fig. 2 are homologous with the first
two free caudals in Rallus aquaticus and Ocydromus australis. The parapophyses of
the seventeenth and eighteenth sacrals expand, coalesce (a small foramen intervening),
and unite with the "deck" (v), of which they form the inner beginning. The par-
apophyses of the first caudal in Rallus abut against the ilia, leaving a small intervening
foramen between them and the antecedent parapophyses. The homologous foramina
are seen on each side of the vertebra ¹⁹ in fig. 2. P1. LXXXVIII.

From these foramina each ilium extends backward 2 inches. The free terminal ends
bend slightly toward each other, leaving an interval of 9 lines; they are obtusely
rounded. Externally each is strengthened by a vertical ridge (P1. LXXXIX. fig. 1, l).

The entire length of the ilium, following the upper curve, of Aptornis defossor is
12½ inches, equalling that of the same part of the pelvis in Casuarius bennettii. This
length is pretty equally divided by the mesial beginnings of the "gluteal ridges"
(P1. LXXXVIII. fig. 1, g).

The fore half of the ilium repeats very closely the characters of that part in Aptornis
otidiformis². The upper curve is greater in Aptornis defossor; the gluteal ridge is
stronger, runs more outward, and ends by an obtuse process (P1. LXXXIX. fig. 1, h).
The rest of the pelvic disk (P1. LXXXVIII. fig. 1, r, r) is bounded externally by the

¹ In my 'Anatomy of Vertebrates,' the statement (vol. ii. p. 227) that "the kidneys are more or less
blended together at their lower extremities in the Coots (Fulica)" will probably bear the above explanation.
² P1. LXXXV. fig. 1, P1. LXXXVI. fig. 1.