196 Mlt. W. P. PYCKAFT ON THE MORPHOLOGY AND 



by the exoccipital portions of this condyle, which meet in the median line above it. 

 Seen dorsallj', the basi-occipital is cut off from the pro-otic 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 Aj)teryx australis mantelH it agreed very closely with that of 

 Drotmens, 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 

 Bromceiia 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 Bromwiis, Casii- 

 ariiis, and Apteryx, and by the squamosal only in Bhea — this last, in Bhea, 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-otic articulation for the quadrate. 



Internally, the exoccipital is almost entirely concealed by the opis- and pro-otics. 



The sitpra-occipitaJ, in Di'oma'us and Rhea, runs upward and forward in the form of a 

 blunt cone ; in Apteryx the superior border is gently hollowed. In Dromwirs, Casuarivs, 

 and Apteryx it is cut off from the squamosal by the exoccipital ; in Bhea 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 Apteryx and Dromwifs, it has fused 

 with the pro-otic. 



The pro-otic, even in the youngest Ajiteryx (PI. XLIII. fig. 3) and Lroirueus 

 (PI. XLIII. 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). 



