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Show 1905.] OSTEOLOGY OF THE EU R Y L iEM ID ^. 41 of the spatulate process lies on a level with, but mesiad of, the external aperture. Without this chamber is a large sinus roofed by the rhamphotheca, floored by membrane supported by the maxillo-palatine process, and closed posteriorly by the antorbital plate lying external to the nasal chamber. In the dried skull this sinus is included as part of the external narial aperture. The quadrate, though not yet completely ossified, differs in no material particular from that of the adult. b. The Membrane-bones. The parietal is roughly quadrangular in shape ; its superior external angle is drawn upwards into a point, its inferior external angle forms a sweeping curve. Its mesial border is not yet ossified in. the skull now described. A small portion of its inferior border, lying between the supraoccipital and squamosal, comes into actual contact with the exoccipital. The frontal along its posterior border follows the curve of the parietal: anteriorly, in the mid-orbital region, it becomes reduced to a narrow band, and finally terminates in a strap-shaped process underlying the nasals. Before leaving the cranial cavity its free edge passes downwards and inwards to join the alisphenoid inferiorly. The rim of this inturned plate is overlapped by a long tongue-shaped process of the squamosal (PI. II. fig. 1 a). The squamosal is a somewhat remarkable bone. Roughly JL-shaped, the horizontal region overlaps, mesiad, the lateral occipital and extends so as nearly to reach the supraoccipital; laterad it overhangs the tympanic cavity and terminates in a pointed processus zygomaticus squamosi. The vertical shaft arising from this base is roughly sword-shaped, with a slightly decurved pointed tip. About one-third of this blade arises above the level of the parietal to overlap the frontal as already described. Immediately above the level of the superior border of the alisphenoid this blade develops a barely perceptible prominence, which supports a small cartilaginous nodule-the anlage of the postorbital process. Another most noteworthy feature of the squamosal in this skull is the fact that the greater part thereof appears on the inside of the skull: only, indeed, the extremities of the horizontal and vertical portions being excluded. Compare figs. 1,1 a (PI. II.). In the most primitive types of Avian skull, it will be remembered, the squamosal is either entirely excluded from any participation in the formation of the brain-case, or only a very small area is admitted. Originally a quite superficial bone, it has gradually absorbed the underlying osseous tissue, till eventually it has forced itself into the very walls of the cranial cavity, and this is especially the case in the skull of Eurylcemus ochromelas. I am unfortuately unable at the present time to make any extensive series of comparisons between the form of the squamosal in the Eurykemidte and that of the Coraciiformes, or the |