No. I.] THE CRANIUM IN THE OWLS. 143 



is symmetrical for the two sides, the tensor muscle that closes 

 them, and which transversely divides either auricular opening 

 at about its middle, exhibits a peculiar asymmetry. This 

 muscle arises symmetrically on the right as well as on the left 

 side, near the center of the lid's inner surface, while its 

 attachment, upon either side, to the cranium posteriorly is 

 thoroughly asymmetrical. On the right side the tensor muscle 

 is attached posteriorly, at a point about in the middle of the 

 osseous crest of the os squaviostim, or rather so high up that 

 the entrance to the ear upon this side must necessarily be 

 below the transverse fold formed by the muscle, and that part 

 of the entrance above the muscle consequently closed. On 

 the left side the muscle is directed more obliquely downwards 

 and makes an inferior attachment posterior to the mandible, 

 at the lowest extremity of the osseous crest of the os sqiia- 

 mosum; consequently the aural entrance is found above the 

 muscle, while the lower part of it is closed over. The muscle's 

 attachment to the ear-flap, as already described above, is seen 

 to be upon the inner surface of the latter, near its center, 

 after first having passed and received support from the short 

 but distinct process which occurs upon the posterior aspect of 

 the osseous crest of the alisphenoid. 



In addition to the tensor muscle proper, there is a feebler 

 one lower down, which, upon either side, passes from the 

 mandibular border to the lid's inner surface, in the direction 

 of the gape of the mouth. 



The nostrils are oblong, elevated, close together, and com- 

 paratively large, besides being longer than they are high 

 (length 6 mm.; vertical diameter 4 mm.). 



That part of the beak posterior to the nostrils, and covered 

 by the cere, is somewhat raised and of oblong form. The 

 cranium, which does not exhibit any notable asymmetry, is, if 

 viewed upon its superior aspect, seen to be strikingly pointed, 

 or almost triangular, inasmuch as such parts of the margins 

 of the orbits formed by the frontals are obliquely sculptured ; 

 therefore the postorbital region of the cranium is more con- 

 tracted, and lacks the rounding off which takes place in the 

 other groups. The greatest vertical height of the cranium is 



