244 MR. G. P. MUDGE ON THE MYOLOGY 



seven belong to the most primitive stages, and the other two are not very much more 

 advanced. And it is interesting to note that Ueroptyiis and Conurns ho/or/dontf>, 

 although i)laced with I'siUacus and Coracojms in respect of the character of the 

 inferior ceratogh)ssal tendon, are intermediate between them and the members of 

 column II. in the remaining characters of that muscle, which is a position they should 

 occupy if my interpretation of the nature of the parahyal fibres of their thyro- 

 glossus muscle is correct. In Poeocephalus, the thyroglossus of which, according to 

 the meaning here attached to it, is the most advanced of Stage 4, the characters 

 of the inferior ceratoglossal are identical with those of some of the Parrots in 

 column II. 



To state the facts in a briefer form, we may say that there are two sets of Parrots 

 with a parahyal process origin for the thyroglossus. In one of these sets the cerato- 

 glossus inferior is primitive and in the other specialized. Hence has arisen the 

 conclusion that the parahyal process origin in the one case is primitive and in the other 

 secondary. And, seeking for a logical demonstration of the truth of this conclusion, 

 we must find a Parrot which in respect of its ceratoglossus inferior must be inter- 

 mediate between the two sets of Parrots, and in the characters of its thyroglossus 

 must show the transition from the entoglossal origin — which has been traced from 

 the primitive parahyal process stage — to the secondary parahyal process stage : such 

 Parrots are Beroptyus, Conurus holochlorus, and Poeocephalus ; and they exhibit, as far 

 as the first half of the gap, a graded series. 



The conclusion is further corroborated by a consideration of the amount of extension 

 of the hypoglossus obliquus. In those Parrots in which I regard the thyroglossus 

 origin at the parahyal process as being primitive, the hypoglossus obliquus is limited 

 to the head of the hypobranchial, and in two instances only extends back along that 

 through the anterior third ; but in those in which the parahyal process origin is 

 secondary the hypoglossus obliquus extends backwards along the whole length of the 

 hypobranchial in the majority of instances, and in only a few as far as the anterior 

 two-thirds. 



If the conclusion that the parahyal process origin of Stages 5 and 6 of the thyro- 

 glossus is not accepted, the only other alternative is to believe that this muscle has 

 remained primitive in Parrots in which other muscles have advanced to a specialized 

 condition, and that it has advanced to more or less specialized conditions in Parrots 

 in which other muscles have remained primitive or have advanced but slightly. 



The evolution of the muscle is graphically represented in the following Table : — 



