OF THE TOKGUE OE PAEEOTS. 219 



slightly thickened tract that is prolonged backwards, and serves as an origin for the 

 ceratoglossus inferior posticus (PL XXVIII. figs. 21 & 28). This tract is part of the 

 substance of the ventral fascia of the muscle and cannot be separated from that without 

 injury ; it is not, therefore, an individual structure. 



The ventral fascia of the muscle at this stage is still uniformly tendinous (PI. XXVIIT. 

 figs. 27 & 28), and in its general features resembles that of the earlier stages. 



In Ara macao (PI. XXVIII. fin;. 27) the ceratoglossus inferior posticus {cg.i.p.) 

 extends along the hypobranchial (HB.) for the anterior third only, and the inner portion 

 (cg.i.a^.) of the ceratoglossus inferior anticus does not reach quite to the urohyal, but in 

 other respects is well developed. Unlike that in Ara ararauna, there is a cerato- 

 glossus inferior anticus accessorius (c(/.i\). Microglossus aterrimus is similar to Ara 

 ■macao, but the ceratoglossus inferior anticus accessorius is very small. 



Cacatua trifon, in respect of this muscle, is in its general features similar to other 

 species of Cacatua, but in addition it possesses the characters which belong to this 

 stage. It, however, deviates from this stage and belongs to that of the earliest in 

 the great development of the inner portion (cg.i.a\) of the ceratoglossus inferior 

 anticus, which is even more strongly developed than in Cacatua alba ; it shows no 

 signs of retrogression. The ceratoglossus inferior posticus extends backwards along 

 the anterior third of the hypobranchial. 



In Cyanolyseus patagonicus the muscle is like that in Ara macao, but the cerato- 

 glossus inferior anticus accessorius (cg.i^.) has almost disappeared. 



In Chrysotis oclirocephala (PI. XXVIII. fig. 28) the muscle resembles that of Ara 

 macao, but the ceratoglossus inferior posticus {cg.i.p.) extends farther along the hypo- 

 branchial, reaching to the end of the anterior two-thirds, and the inner portion [cg.i.a^ .) 

 of the ceratoglossus inferior anticus has undergone considerable retrogression in such a 

 way that the lateral half of its inner part has disappeared. I propose to indicate this 

 amount of retrogression by the numeral II ; when, as in other cases, the whole of the 

 inner portion has disappeared by the numeral III ; when the extension on to the 

 urohyal has disappeared and the inner lateral retrogression is not greater than in 11, 

 by I ; and the fully developed muscle by O. The ceratoglossas inferior anticus acces- 

 sorius [cg.i^.) is very large, and arises from almost the whole length of the uro-hypo- 

 branchial tendon. In Chrysotis ijanamensis, C. cestiva, and C. viridigena the muscle is 

 similar to that in C. oclirocephala, but the thickened tract in the tendinous fascia 

 is slightly more pronounced, and tends to approach the condition of that in the next 

 higher stage ; the ceratoglossus inferior anticus accessorius is like that in Ara macao. 

 In C. panamensis the ceratoglossus inferior posticus only extends one-half of the 

 length of the hypobranchial, and the inner portion of the ceratoglossus inferior anticus 

 is more strongly developed, noc having retrogressed beyond stage I. 



VOL. XVI. — PART V. No. 2. — October, 1902. 



