1905.] OSTEOLOGY OP THE EDRYL^BIID^. 41 



of the spatulate process lies on a level with, but mesiad of, the 

 external apei'ture. 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 extei-nal to the nasal chamber. In the diied skull 

 this sinus is included as part of the external narial aperture. 



The quadrate, though not yet comj)letely ossified, difiers in no 

 material particular from that of the adult. 



b. The Membrane-hones. 



The jmriQtal is roughly quadraiigular 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 desciibed. A small portion of its inferior 

 border, lying between the supraoccipital and squamosal, comes into 

 actual contact with the exoccipital. 



The /ro«to^ 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 

 inferioi'ly. The rim of this inturned plate is overlapped by a long 

 tongue-shaped process of the squamosal (PL II. fig. 1 a). 



The squamosal is a somewhat remarkable bone. Roughly 

 J.-shaped, the horizontal region overlajos, mesiad, the lateral 

 occipital and extends so as nearly to reach the supraoccipital ; 

 laterad it overhangs the tympanic cavity and terminates in 

 a pointed jjrocesstcs 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 desciibed. 

 Immediately above the level of the superior border of the ali- 

 sphenoid this blade develops a barely perceptible j)i'ominence, 

 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 pai't thei'eof appears on the 

 inside of the skull : only, indeed, the extremities of the horizontal 

 and vertical portions being excluded. Compare figs. 1,1a (PI. II.). 



In the most primitive types of Avian skull, it will be re- 

 membered, the squamosal is either entii'ely 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 squa- 

 mosal in the Euryltemidse and that of the Coraciiformes, or the 



