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the end of the tuberosity 1 inch 4 lines; the breadth of the tract is 1 inch 4 line: in 
the centre of the tract is a small venous foramen. The tuberosities bend forward and 
inward; cach is indented by an oblique channel; and from each a nidge continuing the 
convergence is lost after 3 lines course upon the fore part of the basisphenoid. This 
curyes 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. LX XXIII. fig. 3, 9). The occipital foramen (Pl, LXXXIV. fig. 1, 0) 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'. The vertical 
diameter of the foramen is 7 lines, the transverse one 64 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. LX XXIII. fig. 2, 3). 
From the under and inner base of the paroccipital an irregular ridge or bar of bone 
(Pl, LX XXIII. 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 hke 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 otidifornis: 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 grooyve-like extension of the tympanie 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 Cuyier’s “ temporal” in birds agrees with the 
mammalian mastoid, Mr. Parker admits that the mastoids are already ossified at the 
“time that the parictals 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 cartilage, 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. ‘he 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 pheumatic yacuities and the canal for 
1 Pl, XLII. fig, 4, 0, 


