1895.] HTOID BONE OF CEETAIN PAimOTS. 165 



of the bony isthmus lies, as it were, at the bottom of a bony 

 valley formed by the much inwardly inclined dorsal surfaces of 

 the rest of the two entoglossals. 



Each entoglossal presents a dorsal surface which is slightly 

 concave from within outwards and looks upwards and inwards and 

 is much curved, convex dorsad, antero-posteriorly, especially at 

 and behind the bony isthmus, the part posterior to which has a 

 dorsal surface convex in both directions. The ventral surface of 

 each entoglossal is correspondingly inclined downwards and 

 outwards and is antero-posteriorly concave, while it is slightly 

 convex dorso-ventrally at its anterior portion, the hinder portion 

 being dorso-ventrally concave. Each entoglossal expands slightly 

 towards its anterior end, where it shows a tendency to bifurcate ; 

 the dorsal surface of this most anterior part is concave, while 

 ventrally it is flattened. Postaxially, its end is somewhat D)ore 

 pointed, but does not bend much ventrad at its point. "When seen 

 in profile the dorsal margin of each entoglossal is at first shghtly 

 concave, antero-posteriorly, and then sti'ougly convex. Its ventral 

 margin is nearly straight (with onlj' a rudiment of a ventrad pro- 

 cess), till we come to the anterior part of the descending posterior 

 portion of the entoglossal, where it expands dorso-ventrally, bends 

 mesiad, and joins its fellow of the opposite side. It then rapidly 

 narrows to its hinder end, the expanded part being crossed by a 

 slight antero-posterior ridge concave \entrad. Anteriorly each 

 entoglossal hardly diminishes perceptibly in vertical extent and 

 appears truncated at its termination. 



The posterior side of the bony isthmus, formed by the junction 

 of the entoglossals, presents an articular surface strongly concave 

 from side to side and convex dorso-ventrally. 



The anterior margin of the bony isthmus is strongly concave 

 from side- to side. 



Each liypohrancMal is twice as long as the basihyal. It is stout 

 and much laterally expanded towards its preaxial, articular end, 

 the articular surface of which corresponds with that of the basi- 

 hyal to which it is applied. At the postaxial end of its preaxial 

 third it contracts rather rapidly, and is slender thence till close to 

 its hinder end, where it expands and articulates with the cerato- 

 branchial. The anterior part of the dorsum of each hypobranchial 

 is antero-posteriorly grooved. 



Each ceraiobranchial is in the form of a small flattened ossicle, 

 a little more than twice as long as broad, strongly bent concave 

 mesiad, not tapering tov\ards its termination, which is tipped with 

 cartilage. 



LORIUS DOMICELLA. (Eig. 2, p. 166.) 



Compared with Psittacus erithacus, as regards the structure of 

 the hyoid, Lorius domicella has the hcisihyal more elongated and its 

 posterior part less expanded laterally and less quadrate in shape. 

 The dorsal lip of its anterior articular surface is more elevated (so 

 that its summit is visible when the hyoid is viewed in profile) and 



