138 MEMOIRS OF THE CARNEGIE MUSEUM 



the superior border. It is evident that this otherwise thick jaw is much weakened 

 at these points in each ramus, and this occurs just posterior to the hinder termina- 

 tion of the horny sheath of the lower beak. In other words, the hinder moieties of 

 the mandible are attached to the anterior or dentary portion by thin plates of bone, 

 consisting principally of the splenial elements, and are capable of being bent out- 

 ward, which, in the recent specimen can, owing to the way the quadrates are 

 attached, be effected to a considerable degree. Now in life these oblique slits have 

 their anterior ends come opposite the thin anterior insertions of the maxillaries, 

 and these latter are just beneath the very mobile cranio-facial hinge, so that the 

 whole apparatus is admirably arranged to permit an increase in size of the fore part 

 of the buccal cavity when a Gannet swallows the fish that constitutes its food, and 

 which its beak is so well fitted otherwise to capture. Moreover, this possible 

 increase in caliber takes place in that portion of the digestive tract where it is most 

 needed, or where the bony walls of the mouth would prevent the admission of a 

 very large morsel, unless some such mechanism existed, that is, at the very 

 entrance of the buccal cavity, and just posterior to the more horny thecse of the 

 beak. In Gannets, however, this mobility is, to some extent, restricted by the 

 integumental sheath of the beak. 



Sulidse have a wonderfully pneumatic skeleton, the entire structure enjoying 

 that condition, save the ribs; all the caudal vertebra (with the occasional exception 

 of the anterior one) 1 ; and, finally, none of the bones of the pelvic limb are pneu- 

 matic below the femur. The entire skeleton of the wing is perfectly so. 



In a specimen of Sula gossi before me, nine or ten large sderotal plates ossify in 

 either eyeball, and these overlap each other much as we find they do in other 

 birds. All the tracheal rings ossify quite perfectly, as do the bronchial semirings as 

 they approach the lungs. These rings look like little, narrow, bony, double-over- 

 lapped straps, as they are arranged in situ to form the somewhat antero-posteriorly 

 compressed windpipe. The usual bones of the superior larynx also ossify, and in the 

 syringeal portion of the tube we find strong osseous arcades overarching the com- 

 mencement of either bronchial tube, and parallel to them below, in the median 

 line, the dividing pessulus is also in bone. 



Anatomists have long known that the hyoidean apparatus as found in the Sulidse 

 is invariably a very much aborted affair. The only parts of it that ossify are, first, 

 a little irregular piece which represents the first basibranchial ; and second, articu- 

 lating with this behind, are two simple curved rods of bone, which are the cerato- 

 branchials of the thyro-hyals. Beyond these, no part of the tongue of a Gannet 

 ever appears to ossify. It is hardly necessary to say that such parts of the skeleton 



