or THE TONG-UE OF PAEROTS. 241 



from the parahyal process is confluent with the tendon of the stylohyoideus at its 

 insertion on the apex of the parahyal process. 



In Poeocephalus ruppelli (PI. XXVI. fig. 10) the entoglossal portion (tk.g^.) of the 

 muscle is split into two branches, and is similar to that described for Ptistes {ante, 

 p. 240). Of the two branches, the smaller one takes its origin from the entoglossal 

 of the same side, while the much larger one passes over to the entoglossal of the other 

 side, and arises from this at its posterior extremity by an origin common to it and 

 the smaller branch of the muscle of the other side. Thus the muscle at its origin from 

 the entoglossal of either side consists of two sets of fibres : of a larger set derived 

 from the muscle of the other side and a smaller set derived from the muscle of the 

 same side ; the fibres of the two muscles are thus distributed and cross each other in 

 precisely the same way that the nerve-fibres of the optic tract of mammals do. The 

 parahyal portion {th.g.) of the muscle is smaller than the combined entoglossal portion. 

 In P. rohustus there is the same general arrangement and optic-chiasma-like condition 

 of the muscle ; but the parahyal portion is larger than the entoglossal, and the larger 

 branch of the entoglossal part belongs to the same side and the smaller to the other 

 side, which is just the reverse to that in P. riippelli. 



The condition which the muscle exhibits at this stage (Stage 4) may be interpreted 

 in two ways : either the parahyal portion is retaining, to a greater or less extent, 

 its primitive relation to the parahyal process, or, it is secondarily coming back 

 to it after it had attained a wholly entoglossal origin. It is necessary to decide, as far 

 as possible, which of these two alternatives is the more probable ; and since the answer 

 depends upon the condition of the muscle in the later stages of its evolution, I shall 

 proceed first to their description. 



Stage 5. 



The relations of this muscle at this stage are somewhat similar to Stage 1 in Method B. 

 It arises from the apex of the parahyal process, and is inserted into the dorso-lateral 

 surface of the thyroid. It tlius corresponds in its origin, and nearly so in its insertion, 

 to that in Coracopsis, which I have placed at a much earlier stage ; but there is a 

 difference — which, however, does not hold true in ail cases — in that at this stage the 

 insertion of the thyrohyoideus is distinctly ventrad of the thyroglossus, whereas in 

 Coracopsis the two muscles run an almost coincident course, not only at their insertion, 

 but along their whole length. The further reasons that have induced me to consider 

 similar conditions as belonging to two distinct stages I shall mention later {infra, 

 p. 243). 



Platycercus eximius (PL XXVI. fig. 11, th.g.) may be taken as typical of this stage; 

 the thyroglossus arises from the apical region of the parahyal process dorsad of that of 

 the thyrohyoideus, and retains this position with respect to the latter muscle along its 

 whole course, including its insertion. If it be compared with that of Coracojjsis 

 (PL XXVII. fig. 17) the diff'erence in its relation to the thyrohyoideus is apparent, for 



