OCR Text |
Show 1905.] OSTEOLOGY OP THE EURYL/EMIDiE. 35 The cerebral fossce are relatively of considerable size, though relatively smaller than in Corvus for example. Thus, in the Eurylaemidae the cerebral fossa is only distinguishable from the mesencephalic fossa by reason of the boundary-line of the tentorial ridge. In Corvus the mesencephalic fossa forms a totally distinct basin-shaped cavity, lying as it were within the cerebral fossa, which dips down to the outer side and below the level of the fossa in question in the form of a deep pocket. Menura represents a half-way stage between the Corvidae and Euryltemidae. In Menura, moreover, the roof of the cerebral fossa is marked by a low ridge roughly dividing the fossa into two equal parts. There is a well-developed bony falx. The olfactory fossae are reduced to a pair of small pits. But there are strong impressions of an olfactory tube to be found in the fore part of the cerebral fossa of the Eurylaemidse. The Premaxilla. The premaxilla in the Eurylaemidae forms the major part of the upper half of the beak. Hooked at the tip, and of extreme breadth, it recalls in many respects that of many of the Coraciidae, e. g. Eurystomus, on the one hand, and of some Caprimulgi, e. g. Podargus, on the other. When these several types come to be compared, however, these resemblances will be found to be but slight. More significant is the close resemblance to the Cotingidae. This is well brought out in the skull of Calyptomena, which, as will be shown presently, presents many features in common with Chasmorhynchus. The number of other skeleton characters which these two forms possess in common suggest affinity between the two groups, rather than liomoplasy. In Calyptomena, which I propose to take as the typical Eurylaemid for the purpose of comparison, the body of the premaxilla is moderately large. The nasal process, fusing with the nasals, is sharply truncated caudad, and articulates with the fi-ontals by a hinge. In this respect the Eurylaemid skull resembles that of the Podargidae, and not of the Coraciidae. The low position of the skull of Calyptomena is indicated by a comparison of the narial aperture with that of the skulls of other Eurylaemid genera. In Calyptomena the nasals are of the typical holorhinal shape with an obliquely sloping descending process. The nasal fossa, in the dried skull, is a long oval aperture showing, within the cavity, a narrow ridge of bone continued from the palatal border forwards to meet a low septum hanging from the middle line of the nasal process of the premaxilla. The septum represents the ossified remains of the septum nasi; the small plate of bone running inwards from the level of the tip of the palatine is a portion of the alinasal cartilage which has become ossified. |