OCR Text |
Show 1028 MR. W. P. PYCEAFT ON THE [Dec. 19, form of the coronoid. This is long, narrow, and pointed. Its anterior half remains distinct throughout life, the posterior region fuses with the angulare. The dentary suture also remains distinct. In the Divers the supra-angular is pierced by a large foramen, which remains permanently open : furthermore the jaw may be distinguished from that of the Grebes by a deep notch situated immediately behind the outer border of the glenoid surface for the external condyle of the quadrate; in this last it agrees with many Alcidae. The internal angular process is feebly developed. The mandible of the Podicipides (Grebes) lacks the notch just described, and the foramen piercing the supra-angular is much reduced in size, aud shut off from within by the base of the coronoid; the internal angular process is moderately well developed. The Hyoid. The hyoid of the Pygopodes differs markedly from that of the Alcidas, both in the form of the basihyal and basibranchial ossifications, neither do they bear any close resemblance either to those of the Tubinares or of the Impennes. In each of the three last-mentioned groups the first and second basibranchials are anchylosed, the latter being continued backwards in the form of a median pointed bony style between the ceratobranchials to form the "urohyal." In the Pygopodes the first and second basibranchials appear to remain distinct throughout life. In the Pygopodes the first basibranchial-the main body of the bone-takes the form of an oblong plate hollowed dorsallv, and with a slight median keel ventraily. The basihyal is partly ossified, the ceratobranchials are relatively very lono-, the epi-branchials short and slender. In the Colymbi the first basibranchial takes the form of a flattened oval, and the anterior region of the ventral median keel is strongly developed. The second (" urohyal") is apparently but imperfectly ossified, only the very centre of the rod-shaped style being bony. In the Museum skeletons there is no basihyal ossification, but this may have been lost in maceration. iii. THE SKULL OF THE NESTLING. T ?°V f.he^est}iuS which forms the subject of the following notes I have to thank the Hon. Walter Bothschild, who kindly provided it specially for this purpose. a. Cartilage-bones. The basioccipital seen externally is linguiform ; it forms the centra portion of the occipital condyle posteriorly, and anteriorly is underfloored by the basitemporal plate of the parasphenoid. It joins the exoccipital by harmony suture. Internally it is sphe"ndQ *V J e^ciPita] and anteriorly by the basi- |