18 MR. W. P. PTCEAFT ON THE 



The quadrate has not yet assumed its fully adult form, the orbital process being 

 still cartilaginous. 



The columella in the older skulls has completely ossified, but stapedial rays are 



not traceable. 



The articular is still separately distinguishable. 



Ilembrane-bones. 



T\\Q x>arietal presents two distinct forms. In Syrnium it may be described as oblong 

 in form, but liaving the infero-lateral angles obliquely truncated by the overlapj)ing 

 of the squamosal. It extends outwards and forwards to the alisphenoid, and divides the 

 frontal from the squamosal. In a half-grown skull of Syrnium aluco the frontal sends 

 down, immediately behind the alisphenoid, a tongue-shaped process to overlap the 

 supero-external angle of the parietal, and thus appears to diminish the distance between 

 itself and the squamosal. 



Bubo, Scops, Ketiqoa, Gymnoscops , Syrnium, and Strix have this parieto-alisphenoid 

 articulation. In Scops, however, tlie skull appears to be undergoing a change in the 

 matter of the relations of the bones of this region, inasmuch as the oblique external 

 lateral border has been cut back so as to cause it to fail to meet the alisphenoid, 

 and allow the squamosal and frontal to meet. 



Speolyto differs markedly from the type seen in Syrnitmi in the form of the parietal, 

 and in the relations of this to the neighbouring bones — alisphenoid, frontal, and squamosal. 

 In Speotyto the superior border of the parietal, instead of being straight, rises upwards 

 and forwards for a considerable distance and is sinuous in outline. Its external lateral 

 border is deep, but separated from the alisphenoid by the whole width of the squamosal. 

 Finally, by the considerable backward extension of the squamosal, the inferior parietal 

 border is restricted to the supraoccipital region, instead of extending outwards above 

 the exoccipitals also. 



'Hie frontal, save in the differences in the relations between itself and the neighbouring 

 bones in the two types just described, differs but little in form in either. Its general 

 conformation can be seen in PI. 2. figs. 7, 8. 



The squamosal, like the parietal, differs considerably in form and its relation to the 

 alisphenoid, frontal, and parietal bones. In Syrnium it undergoes considerable changes 

 in course of growth : in the quarter-grown skull it is pentagonal in form, and bent upon 

 itself so as to present two distinct faces, an external lateral and a posterior ; in the 

 half -grown skull it has become oblong in form and quadrangular. Both stages, 

 however, differ from the squamosal of Speotyto ; for whilst in Syrnium the superior 

 border of the squamosal is gently arched and runs forward beneath the parietal to the 

 alisphenoid, in Speotyto this border suddenly rises, near its middle, to form a large 

 quadrate plate, articulating by a long horizontal suture with the frontal, and widely 

 separating the parietal from the alisphenoid (PL 2. figs. 7, 8). 



The mesial border of the squamosal, as may be seen when this bone is dissected from 

 the skull, turns sharply inwards, forwards, and downwards, the resulting flattened 



