130 . MEMOIRS OF THE CARNEGIE MUSEUM 



columella auris is very long and bent. It has a small, cartilaginous, extra-supra- 

 stapedial process, and a long, attenuated stylohyal." 



On either side, the entrance to the middle ear in Sula bassana, as in others of 

 the same genus, is shallow, and it is situated quite internal to the quadrate bone, 

 while immediately mesiad to it there is a pit of great depth, with its aperture look- 

 ing downwards, and its base in the vault of the cranium, which seems designed for 

 muscular lodgment; the positions of the usual foramina about it are peculiar, and 

 extremely interesting in these birds. 



The bony wings that shield the entrance to the ears are large and tilted up 

 behind. Each one shows the double facet for the mastoidal head of quadrate, the 

 outer one having its inner margin encroached upon by the pit described above. 



The postero-internal angle of either of these wings is connected with the side of 

 the elevated basi-temporal region by a bony bar. This condition can best be seen 

 from a posterior view. When speaking of the orbital cavity I neglected to mention 

 that the upper part of the septum is longitudinally marked, as in most birds, by an 

 open, single groove for the passage of the olfactory nerve to the rhinal space beyond. 

 The exit for it from the brain-case is very small, indeed, and occasionally, in S. 

 bassana, on one side, the bone spreads over it, rendering the nerve track, for a frac- 

 tion of the initial part of its course, tubular. 



The brain-box itself is capacious and notable for its great width over its com- 

 pression in the vertical direction. Its anterior wall looks directly downward and 

 forward, making an angle of about 45 degrees with the horizontal palatine bodies. 

 Seen from behind, the skull shows, above, the extent to which the crotaphyte fossa? 

 approach each other in the median line and the crest that divides them from the 

 occipital area. This latter has the usual form seen among these cormorant-like 

 birds, constituting an arch over the foramen magnum, which occupies the center of 

 a concavity below it. The supra-occipital prominence is here distinguished by a 

 low, smooth median ridge, which traverses this dome-like elevation from the inter- 

 crotaphyte line to the superior periphery of the foramen magnum. 



The plane of this latter aperture is about perpendicular to the plane of the basis 

 cranii. In outline the foramen is broadly elliptical, with the short axis transverse. 

 At its lower margin .we see a large ellipsoidal condyle, with its short axis at right 

 angles with that of the foramen. Below this again are the oval openings in the 

 basi-temporal, spoken of by Parker, with the prominent descending processes of this 

 region flanking them on either side. 



In form, the inferior mandible is spear-shaped, its sides tapering gradually to a 

 sharpened apex. These latter, for the outer aspects of their anterior two thirds, 



