OCR Text |
Show 1 9 0 3 .] OSTEOLOGY OF THE CUCULIFORMES. 2 6 9 The supraoccipital is extremely short antero-posteriorly, and is deeply cleft in the middle of its superior border. Its external lateral border fuses with the lateral occipital; within the cranial cavity it is bounded by the epi- and opisthotic. The small size of the supraoccipital recalls the skull of the Owls, but this of course is but a coincidence. The character will doubtless be found to obtain in the Kingfishers, Bucconidse, and Capitonidse, which have many characters in common with the Cuckoos. The prootic does not appear externally. Within the cranium it occupies considerable space, forming the floor of the mesencephalic fossa, as well as a considerable portion of the lateral walls, of the basin-like metencephalic fossa. It entirely excludes the squamosal from the cranial cavity. The epiotic is only partially ossified, and in such a way that its boundaries cannot be made out. The opisthotic has fused completely with the prootic. The basisphenoid is not visible externally, being underlaid by the basitemj)oral plate. Concerning its internal boundaries,, nothing satisfactory can be gathered from the two skulls in the National Collection, the younger being damaged, whilst in the more adult skull it has fused with the neighbouring bones. The alisphenoid, in the younger of the two skulls, is not yet completely ossified. As a result, between the external ventral angle and the squamosal there is a wide gap, which extends inwards below the inferior alisphenoid border, dividing its outer moiety from the basisphenoid. This gap, when viewed from without, is seen to be filled up by the prootic. Its supero-external angle is produced outwards to form the postorbital process. The orbito-sphenoid is not yet ossified in these skulls. The presphenoid has fused with the basisphenoid. The mesethmoid, in the two skulls now under consideration, is yet incompletely ossified, forming but a linguiform plate ; the interorbital septum formed by the backward extension of the mes-ethmoid having been represented only by cartilage. The anterior border of the linguiform plate is sharply truncated so as not to extend beyond the level of the free end of the parasplienoidal rostrum below and the anterior extremities of the frontals above. This truncation occurs at the cranio-facial fissure, which has cut the mesethmoid into two parts : the one forming the linguiform plate just described, which ultimately forms the interorbital septum ; the other, the septum nasi, which in these skulls is yet cartilaginous. The cranio-facial fissure appears to be peculiar to the neo-gnathine (Carinate) skull; but traces thereof are apparently to be met with in the Palajognathse (Ratita?), inasmuch as, in the skulls of nestlings of Dromceus and Rhea in the Museum Collection, the ossification of the mesethmoid commences, as in the Neognatlise, by the formation of a more or less linguiform plate, and this has its superior border deeply excised, at a point exactly corresponding |