MOKPHOLOGT OF THE OWLS. 3 



downwards along the free border of the tympanic wing of the exoccipital. The ^-^^Trv^ 



lambdoidal ridge can best be traced in the Asionidse and Strigidse, wherein temporal fossae ^^ ~ 

 are wanting. 



The paroGcipifal processes, so conspicuous a feature in Tllica, for example, and slightly 

 developed in the Palconiformes, are practically wanting in the Striges, the exoccipital 

 tympanic wings from which these processes are developed being very thin, and curving 

 forwards to complete the recessus tympanicus anterior. 



The Hoof of the Cranium. — In the Asionidae (including Photodilus) the interorbital 

 region stands out in strong contrast to the portion forming the cerebral roof, by reason of 

 the narrowness of the former and the great Avidth of the latter, which often nearly equals 

 the whole length of the skull. The free edge of this interorbital region is generally much 

 thickened over the anterior region of the orbit, and furthermore this thickened area is 

 produced caudad into a pair of suj^raorbital spinous processes, recalling the supraorbital 

 process of the lachrymal. That portion of the interorbital region lying between the 

 thickened lateral borders just referred to, is also much thickened by pneumatic tissue, 

 developed, apparently, by the inflation of anterior ends of the frontal and the immediately 

 overlapping portion of the nasals. The result, in the adult skull, is peculiar, in that the 

 base of the culmen of the beak — formed by the nasals and premaxillary — looks as 

 though it had been wedged into a spongy mound of bone. In this way an imperfect 

 nasal hinge has been formed. The cerebral portion of the roof, as we have already 

 remarked, is of great width, expanding behind the orbits into a broad tongue-shaped 

 postorbital process, which may extend downwards to within a short distance of the 

 quadrato-jugal bar. The outline of the cerebral region, traced from the supra-foraminal 

 border upwards and forwards into the interorbital region, may be fairly described as 

 3 -shaped, so that the crown of the head is nearly flat. Very shallow tongue-shaped 

 temporal depressions are always traceable in the Buhotiinm, but are widely sejjarated 

 one from another in the median line. 



The roof of the skull in the Strigida? differs conspicuously from that of the Asionidge 

 by reason, partly, of the excessive development of spongy, pneumatic tissue ; and 

 partly, because the width across the skull at the postorbital processes is much less. 

 The width across the interorbital region is relatively somewhat greater than in the 

 Asionidae ; the relations between the beak and the skull also resemble those of the 

 Asionidie, the former having the appearance of being wedged into the latter when in a 

 plastic state, but the resulting nasal hinge is still more imperfect. The cerebral portion 

 of the dome rises up into a blunt cone culminating at the interorbital region, and 

 marked along the middle line by a deep furrow which extends forwards to the base of 

 the beak, and laterally by a shallow depression above the orbits. This depression is 

 crescentic in shape, and extends from the base of the postorbital process upwards and 

 forwards, terminating above the middle of the orbit. A row^ of pits along the arc of this 

 depression marks the position of the larger disc-feathers. Partly on account of the 

 relatively smaller brain-case, which causes the occipital foramen to appear to lie further 

 backwards, and partly because of the great development of spongy tissue, the outline of 

 the cerebral portion of the skull differs markedly from that of the Asionidte. The post- 



1* 



