0¥ THE TONGUE OF PAEEOTS. 261 



have been of a much more extensive nature primitively, but it has retrogressed in the 

 majority of Parrots along its hypobranchial and basihyal portions, leaving only its 

 parahyal process part. 



Geniohyoid Eus. 



In Parrots this muscle has reached a stage not known to have been attained in other 

 birds. In Chauna, Rhytidoceros, Cygnus, Felecanus, Lophophorus, Palamedea, Corvus, 

 Anser, Frocellaria, and Spheniscus this muscle is known to be single. In Nectarinia, 

 Otis, Rhea, Struthio, Dromceus, Rhynchotus, Ciconia, and Opisthocomus it is double 

 (8 & 9). In some Parrots the muscle consists of two divisions, but in the majority 

 it is composed of three, which have arisen from the primitive set of two, by the 

 splitting longitudinally of the anterior one of these. 



The most posterior division of the muscle arises from either the ventral margin of 

 the rami of the mandible (text-fig. 10, ghp), usually about one-third of the way behind 

 the hinder margin of the lower bill, or from the outer surface of the latter (text- 

 fig. 12, p. 251). The two portions of the anterior division arise from a common origin 

 at the inner surface of the antero-dorsal portion of the lower jaw (text-fig. 11, gh.a^., 

 gli.a^.), just posterior to and slightly ventrad of the origin of the mylohyoideus anterior ; 

 they are usually bound together by connective tissue. The posterior portion is 

 inserted into the dorsal surface of the ceratobranchial (PI. XXVII. fig. 12, gh.p.) ; 

 the anterior division of the anterior muscle [gh.a^.) into the posterior extremity of 

 the hypobranchial, folding round its dorsal and ventral surfaces, and the posterior 

 division (gh.a^.) into the ventral surface of the ceratobranchial. 



In Lorius (text-fig. 12, p. 251, and PL XXVII. fig. 21), Eos, Vini, Pnoniturus, 

 Chrysotis cestiva, C. ochrocephala, Poeoceplialus ruppelli, Ptistes, Ara ararauna 

 (PI. XXVIII. fig. 24), Psittacus, Cyanorhamphas, Psephotus, Nasiterna, Eclectus, 

 Loriculus, Paloeornis, Caica, Platycercus, and Tanygnathus the muscle consists of 

 three divisions, the anterior two of which are usually closely bound together with 

 connective tissue at their common origin. In Pnoniturus, Psephotus, Eclectus, and 

 Tanygnathus the outer one of the two anterior portions has developed a small tendon 

 at its origin. 



In Stringops and Brotogerys the anterior muscle is divided into two alono- the 

 greater portion of its length, but at its origin and for some distance behind it is a 

 single muscle. In Pezoporus, Pceocephalus rohustus, Pionopsittacus, Psittacula, and 

 Cyanolyseus the anterior muscle is more or less divided into two in a longitudinal 

 direction. 



In Chrysotis panamensis, Cacatua sulphurea, C. roseicapilla, C. leadbeateri, C. galerita, 

 Calopsittacus, Psittinus, Ara macao, Conwrus jendaya, Bolhorhyndms, and C'alypto- 

 rhynclms the muscle is primitive and consists of only two divisions, a single anterior 



