1888.] PROCEEDINGS OF UNITED STATES NATIONAL MUSEUM. 281 



more or less distinct throughout* life. It is seen reaching forward on 

 the inner aspect of the bone, and seems to be principally designed to 

 hold the splenial element in place, which latter in Diomedea may or may 

 not completely occlude the true rarnal vacuity. Quite a fossa is some- 

 times found posterior to the blade of this fan-shaped process in birds 

 where its handle is more or less individualized. 



These mandibular elements, for flat bones, interlock and cross each 

 other in the most remarkable way in the neighborhood of this foramen, 

 and their stud}- in all birds is a very interesting one. 



The articular cups are very deep at their centers above, culminating 

 in pneumatic pits; the usual circular foramen is also found near the 

 end of the stumpy inner process of this part. 



The facets aud their arrangement are well shown in Fig. 18 and 

 should be compared with others pre- 

 sented, as Sulci, Pelccanus, and the 

 Gulls. 



Posteriorly the hind end of either 

 mandibular limb presents a vertical 

 face, and the angle is drawn down 

 below in a somewhat tuberous, tri- 

 hedral process. 



Only about the proximal third of 

 either ramus seems to be pneumatic; 

 the rest of the bone is dense and 

 solid. 



Of the hyoid arches. — It will be seen 

 from Fig. 20 that these do not very 

 thoroughly develop in an Albatross. 

 The glossohyal and ceratohyals never 

 develop in bone, but are represented 

 in cartilage even in very old birds 

 (D. albatrus), and always remain so. 



A strong antero-median process is 

 developed on the inferior aspect of 

 the first basibranchial, which offers 

 upon its anterior face the articular facet for the cartilaginous glossohyal. 



The body of this basibranchial is subcircular in outline, thick through 

 and through, and co-ossifies with the median spine-like second basi- 

 branchial behind. This latter, like the epibrauchial, is finished off by 

 a cartilaginous tip. 



Articular pits are found, one on either side of the first basibranchial 

 for the heads of the long, slender, rod-like ceratobrauchials. These 

 articulate directly with the short epibranchials, and these are but 

 slightly curved upward behind, as we find them in so many other birds. 



Of the sternum and pectoral arch. — It would be impossible to convey 

 any idea, by means of a drawing alone, of the extreme lightness of this 



Fig» -Id. Fx^. 



Ftg. 18. Articular extremity of right ramus of 

 mandible of Diomedea albatrus; vie wed from 

 above. 



Fig. 19. Anterior portion of mandible, from 

 above; same specimen. Both life size. By the 

 author, from the same specimen shown in Fig. 13. 



