260 STKUCTURE AND CLASSIFICATION OF BIEDS 



sponds to Lathamus. The anterior tendon may represent the 

 fused anterior and middle tendons of Lathaiuus, and the 

 middle tendon may be an extra one, as in Chrysotis. Our 

 reasons for this are that there is a considerable interval 

 between the two tendons, and that they do not diverge, as 

 in all other cases. If this view is correct, the patagial 

 tendons of Psittacus closely resemble those of Chrysotis, 

 while they also agree in having the anterior deltoid larger 

 than the posterior, in the absence of a lower head to the 

 anconaeus, and in having the deltoid completely covered by 

 the tensor patagii. 



The two deltoids are but small muscles, and are largely 

 covered by the relatively enormous tensor patagii. It is 

 better to use the terms ' anterior ' and ' posterior ' for the del- 

 toids, since their relative dimensions vary considerably. The 

 major is ■ by no means always the larger. Sometimes the 

 two deltoids are entirely covered by the tensor patagii, some- 

 times the posterior is partly exposed. Thus in Nestor the 

 muscle is exposed, in Deroptyus and Chrysotis it is covered. 

 In Nestor and Stringops the anterior deltoid is the smaller, 

 in Caica it is the larger. In Tanygnathus, Bolborhynchus, 

 and Eclectus the deltoids are narrow and equisized. In Eos 

 fardinalis the anterior deltoid (which is the larger) is di- 

 visible into two distinct parts. 



As regards the relative sizes of the two deltoid muscles, 

 where they differ, such genera as are known may be arranged 

 as follows : — 



A, Delt. Larger Post. Delt. Larger 



Deropty^ts, Psiftacula, Aprosmic- \ Nestor, Stringops, Calyptorhynchus, 

 tus, Lorius, Caioa, Eos, Fyrrhidopsis, i Cacatna. 

 Lathamus, PalcBornis, Loriculus, 

 Psephotus, PceocepTialus, Cyano- \ 

 rliamphus, Psittacus, Melopsittacus. 



In some parrots the anconmus loiigus has an accessory 

 head from the humerus, which is especially broad in Stringops 

 The table on p. 268 shows the distribution of this accessory 

 head amoiig the genera. 



The expansor secundariorum is stated by Gareod to be 



