No. I.] THE CRANIUM IN THE OWLS. 145 



a symmetrical cranium. Therefore they are enabled to appre- 

 ciate the least evident vibrations of sound far easier than the 

 others, and this, moreover, becomes even still easier inasmuch 

 as they possess, too, such conspicuously large dermal parts to 

 their auricular openings. 



The external border of this osseous crest is quite even, and 

 no process is developed upon it, and, as mentioned above, it is 

 but slightly deflected forwards, so that it does not come quite 

 opposite to the quadrate bone when the skull is viewed upon 

 lateral aspect. Regarding the cranium from in front, the osse- 

 ous crests, in their entirety, project, lateral -wise, beyond the 

 orbital wings (that is, the osseous crests of the alisphenoids). 



Supraoccipital (sqtiama occipitis) has in some specimens a 

 very small supraoccipital foramen, while in others the bone is 

 not perforated at all. 



The pterygoid bones are, especially in front of the basiptery- 

 goid processes {proc. pteryg. oss. sphenoid.), broad and flat, their 

 borders being even and their distal ends presenting extensive 

 and compressed articulatory facets for the palatines. 



The palatines are of medium width ; the pars plana upon 

 either side of the mesethmoid is widely spread out and, if the 

 cranium is viewed from beneath, is seen to come out beyond 

 the externo-lateral margins of the palatines. Vomer present ; 

 usually, but not always, somewhat mesially enlarged. 



The maxillo-palatines are large and come almost in contact 

 in the median plane. 



6. Asio OTUS (Linn.), 1766. 



(Plate XVI, Fig. 12.) 

 Auricular openings and their flaps asymmetrical ; cranium symmetrical. 



The dermal parts of the auricular openings agree exactly 

 with what was found in A. accipitrimis, and the transverse fold 

 (tensor muscle) presents precisely the same asymmetry in its 

 posterior attachment as in that species. On the other hand, 

 the ear-flap, as well as the corresponding posterior fold of integ- 

 ument, is perhaps somewhat a little higher, and consequently 

 the entrance to the ear is larger. This really insignificant 



