322

292

the end of the tuberosity 1 inch 4 lines ; the breadth of the tract is 1 inch 1/2 line : in
the centre of the tract is a small venous foramen. The tuberosities bend forward and
inward ; each is indented by an oblique channel ; and from each a ridge continuing the
convergence is lost after 3 lines course upon the fore part of the basisphenoid. This
curves upward and contracts to a median ridge slightly produced, as a compressed
process, projecting about 2 lines forward freely below the base of the presphenoid
(Pl. LXXXIII. fig. 3, 9). The occipital foramen (Pl. LXXXIV. fig. 1, o) is vertically
elongate, with a small process on each side, projecting inward and forward from the
junction of the lower with the middle third, as in Aptornis otidiformis 1. The vertical
diameter of the foramen is 7 lines, the transverse one 5 1/2 lines, the foramen being rela-
tively smaller than in Aptornis otidiformis. As in that species, the occipital surface,
as it rises from the foramen magnum, slopes forward to the superoccipital ridge
(Pl. LXXXIII. fig. 2,3).

From the under and inner base of the paroccipital and irregular ridge or bar of bone
(Pl. LXXXIII. figs. 1 & 3, 4') passes downward and inward, forming the outer side of
the vagal fossa, and bending forward into and abutting against the smooth deep channel
outside the descending basicranial tract (1-5), where it terminates like an adherent
process, with a rough tuberous ending. It was to the left of these productions
(Pl. XLIII. fig. 6, 4') of the paroccipital, which might be called "styloid processes,"
that the proximal element of the hyoid arch (stylohyal, ib, 38) was anchylosed in the
skull of Aptornis otidiformis: this is significant of the arbitrariness of the ascription of
the tympanic or quadrate bone to that arch. the hind part of the base of the alisphenoid
is more produced and tuberous outside the end of the hyoid process of the paroccipital
in Aptornis defossor than in Apt. otidiformis. Between this process and the expanded
base of the alisphenoid there is a groove-like extension of the tympanic cavity.

The alisphenoid expansion is pneumatic ; in advance of that swelling are two wide
pneumatic openings ; and two lines in advance of these is the foramen ovale.

The mastoid in mammals is characterized by its early ossification, the centre or
centres appearing in the primordial or protocranial cartilage containing the acoustic
vesicle. In this developmental relation Cuvier's "temporal" in birds agrees with the
mammalian mastoid. Mr. Parker admits that the mastoids are already ossified at the
"time that the parietals are small ovoid patches;" but he cannot apparently bring
himself to state that his "squama temporis" in the chick is ossified in and from the
protocranial catilage, including the labyrinth. The "squama temporis" in the human
embryo is ossified in a membranous basis, like the parietal ; the base of the zygoma
alone shows cartilage. The condition of the mammalian squamosal in Monotremes,
in which it is almost reduced to its zygomatic part, shows well the homologous
bone in birds. The mastoid, connate, as usual in birds, with the petrosal, here joins
the alisphenoid, pushing inward, between the pneumatic vacuities and the canal for

1 Pl. XLIII. fig. 4, o.