196 MR. W. P. PYCRAFT ON THE MORPHOLOGY AND 
by the exoccipital portions of this condyle, which meet in the median line above it. 
Seen dorsally, the basi-occipital is cut off from the pro-dtic by a broad patch of cartilage. 
Anteriorly it only just touches the basisphenoid. 
In the youngest Cassowary and Rhea skulls in the Museum collection, the sutures 
of the basi-occipital have almost closed. It takes, however, a slightly larger share in 
the formation of the occipital condyle, inasmuch as it takes a small share in the 
formation of its free border. 
In a half-grown Apterye australis mantelli it agreed very closely with that of 
Dromeus, and, as in this form, the exoccipitals meet in the middle line above the basi- 
occipital. 
The exoccipital, externally, is relatively large. The upper portion of its posterior 
(inner) border bounds the infero-lateral border of the epiotic (fig. 4). The lower 
region of this border is hollowed to form the lateral boundary of the foramen magnum. 
The share which it takes in the formation of the occipital condyle is considerable: in 
Dromeus the right and left plates meeting in the middle line behind the basi-occipital. 
Its dorso-lateral border is bounded by the parietal and squamosal in Dromeus, Casu- 
arius, and Apteryx, and by the squamosal only in Rhea—this last, in Rhea, extending 
backwards to join the supra-occipital. The lower portion of the antero-lateral border 
is free, and in the shape of a large paroccipital process bounds the tympanic recess 
posteriorly. Its internal dorsal angle lies within the tympanic cavity, and helps to form 
the inferior pro-dtic articulation for the quadrate. 
Internally, the exoccipital is almost entirely concealed by the opis- and pro-étics. 
The supra-oceipital, in Dromwus and Rhea, runs upward and forward in the form of a 
blunt cone; in Apteryx the superior border is gently hollowed. In Dromeus, Casuarius, 
and Apteryx it is cut off from the squamosal by the exoccipital ; in Rhea it runs up- 
wards to join the squamosal. That portion of its outer (inferior lateral) border which 
comes into contact with the exoccipital really belongs to the epiotic. In the Penguin 
this last is easily distinguishable, but in the forms now under description it can only 
be made out on a reference to the interior of the skull. 
The epiotic is not indicated externally in the peculiarly distinct manner seen in the 
Penguins ; even in the skull of the youngest of the embryo Apteryxes in our collection 
its only indication is the venous canal which points the boundary line between this and 
the supra-occipital. Internally, it is fairly distinct in all save Apteryx. In all the 
skulls of this collection save those of the embryo Apterya and Dromeus, it has fused 
with the pro-dtic. 
The pro-dtic, even in the youngest Apterya (Pl. XLIII. fig. 3) and Dromeus 
(Pl. XLII. fig. 5) skulls, is not visible externally above the tympanic cavity, being 
concealed by the squamosal. In this it differs markedly from the young Penguin, 
in which a large portion of this bone remains uncovered until the bird is quite 
half-grown (82). 
