OF THE TOJN-GIJE OF PAEEOTS. 221 



extends only one-half the length of the hypobranchial, and is continued forwards 

 beyond the posterior edge of the basihyal to a greater extent than usual, in respect of 

 which it resembles Nasiterna ; the tendinous tract from which it arises is situated on 

 its outer side and not along its middle line. The inner portion of the ceratoglossus 

 inferior anticus (cg.i.aK) has reached stage II in its retrogression, and its posterior 

 extremity is prolonged into a curved finger-like process ; like that in Coracopsis and 

 Ara macao, its anterior portion is covered with a tendinous fascia. 



In Brotogerys 2^yrrhopterus (PL XXVIII. fig. o3) the muscle is different on either side 

 of the tongue, that on the right having the general characters of this stage, in which 

 the ceratoglossus inferior posticus extends to the posterior extremity of the hypo- 

 branchial, while the inner portion of the ceratoglossus inferior anticus has reached 

 stage II of retrogression. On the left-hand side the ceratoglossus inferior posticus 

 shows evidence of a retrogressive atavism, and has gone back to the condition of that 

 in Cacatua galerita (Stage 2), in respect of the fact that it is represented by a posterior 

 extension (cg.i.'pK) of the ceratoglossus inferior anticus, which reaches back as far as the 

 anterior third of the hypobranchial. Behind it there is an elongated conical muscle 

 (cg.P.), originating by its apex from the posterior end of the ventral surface of the 

 basihyal, and inserted by its base along the remaining two-thirds of the hypobranchial ; 

 it is not quite clear what this muscle represents, for, as far as its condition in Brotogerys 

 is concerned, it might equally well be interpreted either as a part of the ceratoglossus 

 inferior posticus or as a dorsal accessory ceratohyoideus. In Psittinus incertus {infra 

 p. 227, &P1. XXVIII. fig. 34) there is a similar condition, but here the muscle can be 

 clearly seen to be a portion of the ceratoglossus inferior posticus, becoming separated 

 from the parent muscle. 



Stage 6. 



In this stage the ventral fascia of the ceratoglossus inferior anticus, though still 

 tendinous, is not so decidedly so as in the last stage, and the tendon derived from it is 

 now more distinctly developed. The ceratoglossus inferior posticus in all cases, with 

 one exception and another partial one, extends back to the posterior extremity of the 

 hypobranchial, and, in respect of that, attains the highest condition of the muscle. In 

 all cases, also, with but two exceptions, the inner portion of the ceratoglossus inferior 

 anticus has attained either stage II or III in its retrogression. 



In Platycercus eocimius (PL XXIX. fig. 44j the muscle reaches its highest development 

 for this stage, the specialized condition of that in Pezoporus excepted. The cerato- 

 glossus inferior posticus extends baekwards to the posterior limit of the hypobranchial 

 (=:-|); the inner portion (cg.i.a^.) of the ceratoglossus inferior anticus has quite 

 disappeared (=111); the ventral fascia is only slightly tendinous, and the tendon 

 derived from it is well developed ; and the ceratoglossus inferior anticus accessorius 

 (C(/.iL) is relatively small. In Pceocephalus ruppelli the muscle is similar to that of 

 Platycercus, but the ceratoglossus inferior posticus extends forwards a little beyond 



2 k2 



