OCR Text |
Show 1899.] OSTEOLOGY OF THE TUBINARES. 393 out life. There is a more or less well-marked vacuity over the lower limb of the dentary suture which is closed by the coronoid. In the Procellariidas there is a more or less well-marked pneumatic foramen opening into the dorsal surface of the internal angular process. In the Dioinedeidae there is a more or less well-marked posterior lateral vacuity which pierces the posterior end of the supra-angular. In D. exulans, immediately behind this vacuity, on the inner side of the jaAv, 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 Avere 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 holloAved. It is produced backwards into a short bony style, from the base of which spring the ceratobranchials. A similar, conical, bony style runs from the anterior border of the fan forwards and at right angles to its long axis. The ceratobranchials are rather more than twice as long as the epibranchials, which are tipped Avith cartilage. iii. THE SKULL OF THE NESTLING. Tbe 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 follovving descriptions are taken are those of very young nestlings of Oceanodroma leucorrhoa. The Cartilage-bones. The cartilage-bones are now, for the most part, more or less completely ossified. The basioccipital Avidens gradually from behind forwards. It is under-floored in front by the basitemporal plate, and bounded on 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 exoccipital.-The upper half of the posterior border of the exoccipital skirts the epiotic ; 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 |