OCR Text |
Show 1899.] OSTEOLOGY OF THE PYGOPODES. 1027 when seen from below. From the dorsal aspect, the trough-like region is found to be restricted to the posterior end, immediately underlying the anterior end of the rostrum. The palatine (Plate LXXII. fig. 7), in its general form, and in its relations with the vomer and maxillo-palatine processes, somewhat closely resembles that of the Alcidae. It differs conspicuously from that of the larger Tubinares iu its greater relative length, and in the feebler development of the paired median and lateral keels formed by the inner and outer borders of the palatine caudad of the maxillo-palatine processes. Its general contour, from the ventral aspect, may be described as rod-shaped, in front of the maxillo-palatines, passing behind these into a shallow trough-like expansion. Seen dorsally, the inner free edge of the expanded portion, cephalad, rises dorsally into a scroll-shaped plate to articulate mesially with the vomer. Seen laterally, this scroll-like dorso-lateral plate does not fit closely up to the posterior border of an almost vertical maxillo-palatine process as in the Tubinares, but leaves a large space between. The pterggoid is rod-shaped, and more or less triangular in section. That of the Colymbi sends outwards, from the outer border of its extreme proximal articular end, a small plate to abut against the base of the orbital process of the quadrate. Moreover, it still further differs from that of the Podicipides, (1) in that it possesses a strong inward curve, causing the pterygoids to embrace the parasphenoidal rostrum, as in many Procellariae, from which it differs, however, in that no glenoid articular surface is developed for this purpose ; and (2) in that it sends forward and upward, from the external ventral border of its extreme distal end, a delicate claw-like process, to embrace the articular end of the palatine- or more correctly of the anchylosed hemipterygoid. This point was first noticed by Coues (3). Tbe quadrate more nearly resembles that of the Tubinares and Impennes than that of the Alcidae. It differs from all in the very elongated and rod-like form of its orbital process. Its otic and squamosal heads are sharply divided. The glenoid mandibular surface nearly resembles that of the larger Tubinares. Its external condyle is hollowed from before backwards; its internal condyle may be divided into relatively large anterior and posterior facets, meeting one another in the mid-ventral line. Immediately dorsad of the posterior facet of the internal condyle is a sharply defined pterapophysial facet for the articulation of the pterygoid. It is non-pneumatic both in the Grebes and Divers, in which point it agrees with both Impennes and Alcidae, and differs from the Tubinares, in which it is pneumatic The Mandible. Is slender, elongated, and slightly recurved at the tip. It can be more or less readily distinguished from that of other groups-such as some Ardeidae, which it somewhat closely resembles-by the |