12 ME. W. P. PYCEATT ON THE 



it emerges immediately beneath the foramen for the first branch of the trigeminal. The 

 foramina for the 1st and 2nd-3rd branches of the trigeminal in the Strigidse.by the way, 

 pass out from a horizontal slit-like foramen on the superior lateral border of the fossa. 

 The abducent foramen, like the oculo-motor, is minute, and lies mesiad and below the 

 inner angle of the fossa for the trigeminal branches 1 and 2-3. It opens into a fossa, 

 immediately behind the optic foramen, which contains besides the apertures of the first 

 portion of the trigeminal and the oculo-motor. Thus, as in the Asionidse, all three open 

 into a common pit. 



The cerebellar fossa presents no chax'acters of any importance. It appears to be 

 slightly larger, relatively, in the Strigidse. The floccular fossa is well-marked. 



The mesencei)haUc fossa apjiears to be relatively largest in Syrnium, and smallest 

 in Strix. In Syrnium and Bubo the boundaries of the fossa are extremely weU- 

 defined. 



The 'pitidtary fossa is relatively much wider in transverse diameter than in the 

 Falconiformes, and differs furthermore therefrom in that its anterior wall rises upwards 

 into a steep wall to pass into a wide but ill-developed optic Y'^diXioyvii{ prepituitary ridge). 

 The preoptic ridge is rounded, swollen and prominent in the Asionidae, ledge-shaped in 

 the Strigidse, and less prominent. At its outer angle this ridge plunges sharply down- 

 wards to join the tentorial ridge. 



The optic foramina are widely separated one from another, owing to the enormous size of 

 the anterior tympanic recess, the anterior end of this great pneumatic chamber lying 

 immediately under these foramina. 



The cerebral fossce have encroached upon the cerebellar fossa, appreciably reducing 

 the size of its upper portion. The tentorial ridge, where it leaves the preoptic platform, 

 plunges sharply downwards to the level of or below the sella turcica, when it sweeps 

 downwards and upwards over the pro-otic, meeting its fellow of the opposite side 

 immediately over the cerebellar fossa. From the point of this union there runs forwards 

 in the middle line a prominent swollen ridge, the bony fals, which is continued forward 

 to form the roof of the olfactory fossa. In the Strigidte the middle region of this ridge is 

 produced into a sharp edge. A more or less prominent ridge corresponding to the 

 Sylvian fissure in the cerebrum is present in all the Striges. 



The olfactory fossce appear to be largest in Bubo, and are never very large. 



The Premaxilla. 



The premaxilla of the Striges is almost indistinguishable from that of the Falconi- 

 formes. It appears, indeed, to differ therefrom only in the greater share which it takes 

 in the formation of the anterior narial aperture, in the nature of the anterior palatine 

 vacuity (which in the Owls is roofed by the ossified alinasal floor, thus concealing the 

 nasal septum), and in that the inner surface of the curved tip is not provided with a 

 median ridge. Seen from the ventral surface, this bone recalls that of the Cathartse. 

 But in the latter both nasal septum and ect-ethmoidal ossifications are wanting, thus 

 revealing the nasal process of the premaxilla, bounded by very long anterior narial 

 apertures — features which in the Striges are conspicuous by their absence. 



