242 ]MK. G. r. MUDGE ON THE MYOLOGY 



ill Flutycercus it is situated dorsally and in Coracopsis laterally to that muscle. In 

 l'sei)hotus scuntltorrhoas, Nymphicus uvceensis, Caica leucogaster, Prioniturus sp. ?, 

 Cyanorhamphus cmriceps, Pyrrhulopsis splendens and P. personata, Psittacula passerina, 

 and Pezoporus formosus (PL XXVI. fig. 8) the muscle is similar to tliat in Platy- 

 cercxis. In Polborhynchus lineolatus the muscle is similar to that in Platycercus, but 

 it is confluent at its origin, and along its ventral border at its insertion, with the 

 thyrohyoideus ; along the remainder of its course it is free of that. 



Stage i). 



In this stage the muscle arises from the hypocleidium (apex) of the completed 

 parahyal arch, and is inserted into the dorso-lateral surface of the thyroid (Pis. XXVII. 

 & XXIX. figs. 21 & 50). It thus differs in respect of its origin from that in Stage 5, 

 in that it arises from the median projecting process formed by the union of the 

 parahyal crura {cf. Mivart, P. Z. S. 6 & 7), instead of from the parahyal processes. 

 Although the muscle (PI. XXIX. fig. 50) lies dorsally to the thyrohyoideus along the 

 major portion of its course, the latter muscle at its insertion turns upwards and, passing 

 between the thyroglossus and the thyroid, becomes inserted into the dorso-lateral 

 surface of the latter. In Eos riciniata the thyroglossus is merged with the thyro- 

 hyoideus at its origin, but otherwise is similar to that in Lorius. In Vini australis the 

 muscle is confluent with the thyrohyoideus both at its origin and insertion. The 

 confluence of the two muscles in these two genera at these particular parts must not 

 be regarded as indicating a primitive condition, for it is probable that this confluence 

 is secondary, and arises from the fact that in these arese the two muscles are in 

 contact. 



A survey of the variations presented by this muscle thus substantiates the statement 

 made {ante, p. 235) that it started along the road of its evolution from three initial 

 stages, all of which ultimately lead to a common stage, the third stage in the evolution 

 of the muscle. Cacatua roseicapilla and C. leadbeateri belong to one of these initial 

 stages, Coracopsis to another, and Brotogerys and Conurus cactorum to the other. 

 Each of these initial stages passes along its own line of development to a second, and 

 each of these converges to a third stage, which is similar in all. This latter stage is 

 characterized by the entoglossal origin of the muscle, and it appears to be, like those 

 that preceded it, but a temporary one, for the muscle, having left the parahyal 

 process to extend to the entoglossum, begins to return to its primitive origin. The 

 flrst step in that return is indicated in Beroptyus accipitrinus, where the origin 

 of the muscle is double ; the greater part arises from the entoglossum, but a few 

 fibres, however, take their origin from the parahyal process. I interpret the parahyal 

 origin as representing the first return of a few fibres back from the entoglossal origin. 

 In Conurus holochlorus a greater number of fibres have returned, and the two origins 

 are nearly equisized. The condition of the muscle in Fosocephalus is fundamentally 

 the same, but its entoglossal portion has specialized in its own direction. From this 



