3 
are slightly concave, have two perforations posteriorly, one above 
and a little in advance of the other, and form the anterior and internal 
boundary of the tympanic cavity. 
In Palapteryx, as in Didus, the basioccipital descends and expands 
into two thick obtuse processes, from which muscles pass to the in- 
wardly-bent angles of the jaw. Internal to these processes are two 
short tubercles. On each side the base of the occipital condyle in 
Dinornis are three small foramina; in Didus two, the outer one the 
largest. 
In Dinornis, Otis and Didus, two foramina, the upper one for the 
hypoglossal nerve, the lower one for the entocarotid artery, open ex- 
ternally in a deep ellipticdepression. The paroccipital is enormously 
developed in Dinornis, and sends a rough thick process from its under 
part to abut against the lateral basioccipital ridge, where it articu- 
lates and sometimes anchyloses with the stylohyal: in Palapteryx 
and Didus the paroccipital carries the posterior surface of the skull 
downwards and outwards in a minor degree than in Dinornis, and 
terminates in a curved convex thick border : its internal surface next 
the tympanic cavity is cellular in Didus. The eustachian outlets 
open, in both Dinornis and Otis, above a transverse ridge terminating 
the basisphenoid anteriorly : this ridge is not present in Apteryx or 
Palapteryx. The Palapteryz also differs from Dinornis in the higher 
position of the precondyloid holes and their greater separation from 
the carotid holes, in the minor development of the paroccipitals, the 
major development of the mastoids, and by the large and single 
oblong depression, beneath the mastoid, for the single superior con- 
dyle of the tympanic bone. In Dinornis the temporal fossa is wide 
and deep, in Didus narrow and deep; the alisphenoid is concave 
where it ascends to coalesce with the mastoid, parietal and post- 
frontal to form the temporal fossa: the limits of the orbitosphenoid 
are also obliterated by a similar confluence: in this region of the 
skull the ‘ foramen ovale’ is preceded in Dinornis as in Didus by two 
smaller foramina, and in front of these is the great ‘foramen opti- 
cum.’ The parietals are very broad and short in both extinct genera; 
but in Dinornis there is a median rising where the sagittal suture 
originally ran, whilst Didus shows a depression and foramen here. 
The mastoid in Dinornis, as in Otis, sends down two processes, one, 
the tympanic process, short,—the other, or proper mastoid process, 
long; this coalesces with the postfrontal in Dinornis, not in Otis : the 
base of the mastoid has two articular cavities for the upper condyles 
of the tympanic bone. In Didus the outer side of the mastoid is 
convex, smooth, but with a slight oblique ridge; it overhangs the 
tympanic cavity, bending inwards, and sends a short compressed 
pointed mastoid process in front of the anterior articular cavity for 
the anterior and upper condyle of the tympanic. 
The presphenoid is a deep compressed plate, thickened and 
rounded below; the palatines abut against it, as in Didus, where 
the fore-part of the pterygoids also rest in part upon the presphenoid. 
The frontals of Dinornis form together a broad hexagonal plate 
moderately convex, with the cerebral hemispheres indicated by very 
