1883.] APPARATUS OF THE TENUIROSTRES. 63 



for comparisou ; they afford an illustration of the fact that similar 

 functional requirements frequently lead to the development of similar 

 structures in animals which are otherwise very distinct. 



The skeletal framework of the hyoid apparatus does not present 

 any important peculiarities. It consists :—(l) of the two pos- 

 terior or long cornua, which are extremely long in the Trochilidse, 

 but very short in Zosterops and Certhia, whilst in the Meliphagidse 

 and in the Nectariniina: their apices do not reach further than the 

 frontal bones ; (2) the basihyal, unpaired and formed by a slender 

 bony rod, bifurcating at each end ; (3) the os entoglossum, which is 

 paired, the two parts articulating with the anterior ends of the basi- 

 hyal, and ending as fine, tapering, more or less cartilaginous rods ; 

 (4) a urohyal, attached to the ventral aspect of the trachea by a 

 short ligament, its anterior portion articulating with the basihyal. 

 This httle bone does not serve for the origin or the insertion of any 

 muscles in the birds in question. The anterior or short cornua have 

 become obsolete. 



In the Trochilidse the basihyal is extremely thin and short, whdst 

 the urohyal seems to be generally absent, and the long cornua and 

 the entoglossal bones are very long. 



The horny sheath surrounding the os or ossa eutoglossa, and pro- 

 jecting more or less in front of them, exhibits very great differences 

 in the various groups of Tenuirostral birds. 



The simplest form is represented hy Zosterops (Plate XVI. fig. 2). 

 The tongue ends in two short filaments, whilst the greater portion 

 of the tongue proper is not divided; dorsal and ventral aspect 

 smooth, hiiider portion of horny sheath projecting backwards with a 

 few (about 3-4) horny spines. 



In Certhia the tongue corresponds with the length of the bdl ; 

 its lateral margins are transformed into sharp cutting-edges ; the tip 

 is frequently split into three short bristles of irregular shape ; the 

 posterior margin ends much as in Zosterops. Along the middle 

 line on the upper surface of the tongue we notice a slight depres- 



sion 



"Whilst in the two genera described above the horny sheath of 

 the tongue shows still a very simple formation, it has in the following 

 families been developed into a very complicated and elaborate organ. 



In order to ascertain the formation of the tubular tongues of the 

 Nectariniina: and Meliphagince, I have made a series of transverse 

 sections through that organ in Nectarinia sjilendida, Cinnyris auri- 

 ceps, Aiithothreptes malaccensis, A. subcollaris, Prosthemadera, Pli- 

 lotis carunculata, and, for comparison, of a species of the Trochilidae. 



The accompanying drawing (fig. 1, p. 64) represents a series of 

 eight stages of the tongue oif Cinnyris, whilst figures 8 and 10 of 

 Plate XVI. show the entire tubes as seen from the ventral side. 



Near the root of the tongue, i. e. near the basal part of the os 

 entoglossum, the dorsal and ventral halves of the horny sheath with 

 which the tongue is covered project to the right and left sides, so as 

 to form sharp, more or less cutting-edges. A httle more in front, 

 hese lateral parts are shghtly curved upwards, the ventral sheath 



