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Show 32 MU. W. P. PYCRAFT OX THE [May 2, the base of the beak it expands considerably and is supported fiom within by outstanding antorbital plates. Lachrymals, except in Calypt'omena, are absent, and consequently take 110 share in the formation of the preorbital region of the skull. In this particular the Eurykemidse agree with the bulk of the Passeres, in which, however, vestiges of the lachrymal are frequently present. The frontals terminate abruptly in front, not extending beyond the level of the anterior border of the mesetlimoid. The nasals and nasal-processes of the premaxilla are also sharply truncated caudad; thus, at their meeting with the frontals and mesetlimoid a freely moving nasal hinge is formed (PI. II. figs. 2 b, 3 a, 4). The incipient stages in the development of such a hinge can be studied in Chasmorhynchus-one of the Cotingidse. The Base of the Skull. The basitemporal plate is slightly hollowed in the middle line, and is continued forward for some distance on to the parasphenoidal rostrum ; owing to the small size of the brain its free edge projects beyond the level of the brain-case. To appreciate this point the skull of one of the Eurybemidae should be compared with say that of Menura or Corvus, where, it will be found, the basitemporal plate fails to conceal the brain-case when the skull is seen from below. The edge of this plate is free only at its apex. Not even vestiges of the basipterygoid processes remain. The parasphenoidal rostrum is long and slender. The occipital condyle is spherical and depends from the roof of a shallow pre-condylar fossa. The Lateral Aspect of the Cranium. (PI. II. fig. 2.) The tympanic cavity is small, shallow, and has little or no floor. The constriction of the skull-wall in the temporal region, to form the " temporal fossa?," gives the tympanic cavity the appearance of the aperture of a tube, the cylinder of which is formed by the " squamosal prominence" and lateral occipital wing. The roof of this cavity is formed by the under surface of the processus zygomaticus squamosi. Its floor in part by the lateral occipital wing and in part by the ossification of tissue extending between this wing and the external angles of the basitemporal plate; but this region is much cut away. Within the cavity three apertures will be found in the dried skull after the removal of the tympanic membrane. The largest of these is the mouth of the recessus tympanicus anterior. Immediately outside this, and below the otic articular surface for the quadrate, is the fenestral recess : this is very small, and neither the fenestra ovale nor the rotunda can be distinguished within it, though the columella is in position above; and behind the fenestral recess a cluster of minute pneumatic apertures will be found, corresponding to a similar group commonly found in the higher |
