1905. | OSTEOLOGY OF THE EURYLEMID. 4] 
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 guadrate, 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 sguamosal is a somewhat remarkable bone. Roughly 
i-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 squamost. ‘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 ali- 
sphenoid 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@ (PI. I1.). 
In the most primitive types of Avian skull, it will be re- 
membered, 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 Hurylemus ochromelas. 
I am unfortuately unable at the present time to make any 
extensive series of comparisons between the form of the squa- 
mosal in the Hurylemide and that of the Coraciiformes, or the 
