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Show 1895.] HYOID BONE OE CEETAIN PAEBOTS. 163 "always short, usually extending forwards from its attachment as well as backward," adding that "the forward production often unites with its fellow, so as to form the basal part of the direct support of the tongue." Each entoglossal does project both more or less backwards as well as forwards from its place of attachment to the basihyal, and this may indicate that it includes a ceratohyal element, but it must surely represent the glossohyal also. This question I will not, however, now attempt to determine. That the Parrots should have a tongue-bone of exceptional form is, of course, only what was to be expected from the exceptional form of their tongue as a whole. I will now first describe the hyoid of Psittacus erithacus as a type, then those of the three genera of Lories and that of the genus Stringops. PSITTACUS EBITHACUS. (Fig. 1, p. 164.) The basihyal is narrow for rather more than its anterior half, expanding slightly both laterally and vertically towards its extreme anterior end, where there is a saddle-shaped surface (for the ento-glossum) convex transversely and concave vertically. Its ventral lip projects forwards much more than does its dorsal lip. On the dorsum of the basihyal at its anterior end is a slight, though marked, concavity (c). The posterior part of the basihyal expands into a subquadrate plate, the centre of which is traversed by a strong antero-posterior ridge continuous with the transversely convex upper surface of the narrow anterior portion of the bone. From each antero-external angle of the quadrate plate of the basihyal a marked parahyal process (p) extends forwards, upwards, and slightly outwards, then narrowing to a bluntish point which inclines inwards as well as upwards, the whole parahyal process on each side being more or less curved. The ventral surface of the basihyal is also strongly convex from side to side at its narrow portion and also along a ridge which thence continues antero-posteriorly across its expanded part and on into the urohyal. O n either side of this median ridge the under surface of the expanded part is gently concave. The hinder border of the basihyal, on either side of its continuation into the urohyal, presents an elongated articular surface, concave transversely, slightly convex dorso-ventrally, for junction with the hypobranchial. The urohyal is one with the basihyal and continues on without change of direction, tapering a little, to its somewhat blunt, slightly enlarged termination, which is tipped with cartilage. Its dorsal margin appears slightly concave antero-posteriorly, when the urohyal is viewed in profile. Its length is three-quarters the length of the basihyal. The entoglossum consists of two lateral parts (entoglossals), which meet together to articulate with the saddle of the basihyal and so form a little transverse isthmus of bone, whence each entoglossal 11* |
