10 MR. W. P. PTCEAFT ON THE 



with that of the Falconiformes, being relatively very short antero-posteriorly, and in 

 some genera enormously thickened by the development of spongy tissue. It is relatively 

 largest in Siirnia and Speotyto : a fact which can best be realized by comparing the 

 mesethmoid of either of these genera with that of, say, Bubo, Aslo, or Syrnimn. In the 

 last-named genera the anterior free border is sharply trraicated, sloping obliquely back- 

 wards to jiass into a remarkably abbreviated parasphenoidal rostrum (p. 5) immediately 

 above the pterygoidal articulation. In Stirnia the parasphenoid extends considerably 

 further forwards, passing insensibly into the anterior border of the mesethmoid at a point 

 corresponding with the level of a line passing behind the lachrymals. The liorizontal 

 plate of the supero-auterior angle of the mesethmoid is not much developed, in conse- 

 quence of the slight development of the olfactoi'y cavity. The antorbital plate 

 (prefrontal) in Siirnia and Speotyto is short and strap-shaped and projects from the 

 inferior angle of the mesethmoid. In Bubo it appears to arise rather below the middle 

 of the anterior border, an appearance which is due to the fact that the anterior border of 

 the mesethmoid by its greater obliquity projects further downwards. In Asio the 

 antorl)ital plates are very long, nearly touching the lachrymals and quadra to- jugal bar. 



The Strigida; differ conspicuously from the Asionidse in the form of the mesethmoid. 

 One of its most conspicuous features in the adult skull is its eiiormous thickness, due to 

 the great development of spongy, pneumatic tissue. The interorlntal region, in addition 

 to its great thickness, is relatively shorter than in the Asionidpe, whilst the olfactory 

 region is relatively longer, and is furthermore peculiar in that its inferior border lies 

 almost horizontally rather than obliquely. The antorbital plate is also much swollen, 

 so much so as to become club-shaped. The interorbital septa, however, of Asio and 

 Photodilus are exceptional, being swollen by pneumatic tissue as in Strix, though to a 

 slighter extent. 



The olfactory cavity is fairly spacious, but contains no turbinal ossifications. Bounded 

 posteriorly by the ali-ethmoidal antorbital plates, it passes forwards into the anterior narial 

 aperture, which is divided from its fellow of the ojjposite side by an imperforate nasal 

 septum. A certain amount of ossification has taken jilace in the ali-ethmoidal walls of 

 the anterior region of the olfactory chamber, the nature and extent of which aj)pear to 

 be best displayed in Surnia, where the cartilaginous portions of the wall, removed by 

 maceration, have left a free edge of bone lying immediately within the anterior narial 

 aperture. Traced inwards, this ossification is fovxnd to have formed a cup-shaped cavity 

 forming the floor of this region of the chamber, and rising upwards, passes into the 

 nasal septum. Posteriorly the wall of the cup is broken down, thus placing the anterior 

 and posterior moieties of the chamber in communication with one another. The external 

 alinasal wall is somewhat more extensively ossified in Asio and Bubo, thus rendering the 

 contour of the nasal aperture formed by the premaxillary limb of the nasal somewhat 

 irregular. 



The floor of the anterior nasal cavity undergoes certain limited changes. Thus in Ninox 

 it is arched instead of hollow, lying above the level of the rim of the narial aperture : in 

 Btibo it is flat ; in Strix it is perforated. The septum nasi is separated from the mes- 

 ethmoid by the crania-facial fissure, which is deep. Furthermore, in some Owls, as in 



