OCR Text |
Show 42 MR. W. P. PYCRAFT ON THE [May 2, Menuvidfe and other Passeriform types, owing to lack of material. Such a comparison I believe would be valuable. So far, the peculiar squamosal of the Eurylaemidse resembles most nearly, among the Ooraciiformes, that of the Capitonidae. But the likeness is but general, and seems to point to the Capi-toniform type as being the more primitive. Herein, this element is roughly quadrangular in type, but has the antero-dorsal angle produced into a point, which, however, does not extend on to the frontal. Its mesial border is, indeed, exactly coterminous with the external lateral border of the parietal. The alisphenoid in this skull is prominent and forms a large triangular block fitting into the deeply concave anterior border of the squamosal on the one hand, and overhung by the postorbital region of the frontal on the other. The postorbital process appears to be formed in part by the alisphenoid, and in part by the frontal. The squamosal takes no part whatever in its formation. These relations can be seen in the skull of Calorhamphus. The resemblance to the squamosal of the Passeriformes is close, but is of a kind such as to leave little doubt but that this element in the EurylaemidaB is much the more specialised : a fact which is somewhat surprising, and is at the same time not without significance. Comparing the squamosal of Eurylcemus ochromelcis with that of the Rook (Corvus frugilegus), it will be found that in the latter this element is of considerable size, conical in form, and rises superiorly to overlap the frontal as in Eurylcemus. The base of this cone is broad, and its postero-internal angle is produced backwards and inwards to form a wedge between the parietal and lateral occipital. It is from a squamosal of this type that the squamosal of Eurylcemus has been derived. This evolution has resulted in a much greater extension of the base mesiad, between the parietal and exoccipital, and in the lateral reduction of the body of the bone so as to transform the sometime cone into a xiphoid shaft springing from a broad base. These changes will become the more apparent by a reference to fig. 1 a, PI. II. The nasal varies considerably in form in this group. Unfortunately, I have not material at my command which will enable me to make a comparison of the early stages of growth of these several varieties. The lachrymal is not yet ossified. The premaxilla apparently lacks palatine pi'ocesses. What appear to be vestiges of these seem rather to be ossifications of the membrane forming the floor of the anterior region of the nasal chamber. This point can only be solved by a further examination of well-preserved material. The maxilla appears to be unusually large in the skull, but the decalcification caused by the formalin in which this specimen was preserved has almost obliterated the premaxillary and quadrato-jugal sutures. |