1899.] OSTEOLOGY OP THE TUBHiTAEBS. 393 



out life. There is a more or less well-marked vacuity over the 

 lower limh of the dentar)' suture which is closed by the coronoid. 

 In the Procellariidge there is a more or less well-marked pneumatic 

 foramen opening into the dorsal surface of the internal angular 

 process. In the Diomedeidae there is a more or less well-marked 

 posterior lateral vacuity which pierces the posterior end of the 

 supra-angular. In D. eA'ulans, immediately behind this vacuity, 

 ou the inner side of the jaw, is a large pneumatic foramen leading 

 backwards below the glenoid surfaces. Furthermore, in this 

 species there is a deep pit, receiving numerous pneumatic foramina, 

 lying immediately behind the articular surface for the inner condyle 

 of the quadrate. The angular is sharply truncated and the 

 internal angular process is very small. 



The Hyoid. 



The hyoid most nearly resembles that of the Penguins and 

 Storks, particularly the former. There is no osseous basihyal. In 

 one skeleton of Pelagodroma marina in the Museum Collection I 

 found a pair of ossified ceratohyals ; these were probably also 

 present in many other skeletons, but have been lost in maceration ; 

 the basibranchial, seen dorsally, is fan-shaped and more or less 

 conspicuously hollowed. It is produced backwards into a short 

 bony style, from the base of which spring the ceratobranehials. 

 A similar, conical, bony style runs from the anterior border of the 

 fan forwards and at right angles to its long axis. The cerato- 

 branehials are rather more than twice as long as the epibranchials, 

 which are tipped with cartilage. 



iii. The Skull or the Nestling. 



The sutures of the skull, unlike those of the Struthious birds 

 and the Penguins, close early. But in very young nestlings the 

 separate bones can all be traced. The skulls from which the 

 following descriptions are taken are those of very young nestlings 

 of Oceanodroma leucorrhoa. 



The Cartilage-hones. 



The cartilage-bones are now, for the most part, more or less 

 completely ossified. 



The hasioccipiiaJ widens gradually from behind forwards. It is 

 under-floored in front by the basitemporal plate, and bounded ou 

 either side by the exoccipitals, from which it is separated by a 

 narrow synchondrosis ; behind, it is rounded off to form the median 

 portion of the occipital condyle. 



The ea:occipital. — The upper half of the posterior border of the 

 exoccipital skirts the epioiic ; the lower is excavated to form 

 the lateral region of the foramen magnum. The share which it 

 takes in the formation of the occipital condyle is a very small one. 

 Its inner border is yet separated from the basioccipital by a 



