258 STRUCTURE AND CLASSIFICATION OF BIRDS 



characteristic of the latter genus. These genera, in fact, are 

 to this extent intermediate between Cacatua and the more 

 normal (at any rate more usual) form of syrinx in the 

 parrots ; the rings are still, however, soft and cartilaginous, 

 thus different from Gonurus, which is a further step in the 

 direction of ChrysoHs ; Chrysotis seems to represent the 

 opposite extreme to Cacatua. Ara is a genus which is 

 also intermediate in the characters of its syrinx; it has 

 weakish and straight rings, as in Stringops, for instance ; 

 hut the muscles are as in the second group of parrots, and 

 the general aspect of the syrinx is more in accord with this 

 placing of it. 



Einally it, should be added that occasionally (e.g. Poly teles 

 ^melanurus) the extrinsic muscles are attached not to the 

 sternum, but to the membrane covering the lungs, being con- 

 tinued there by thin tendons. In Platycercus Barnardi 

 there would seem to be no extrinsic muscles at all. ^ 



Parrots are very much alike in their myology ; there are, 

 however, a few points in which they show differences, and 

 which may be useful for the purposes of classification. 



The tensores patagii of the parrots are like those of 

 many homalogonatous birds in the broad aponeurotic 

 •character of the tendon of the tensor brevis, which, however, 

 has two or three thickened bands in it corresponding to the 

 •discrete tendons of most other birds {e.g. Charadriidse). Of 

 these thickened bands the anterior commonly gives off a 

 wristward slip ; but there appears to be never any patagial 

 fan. The aponeurosis is inserted, as usual, on to the tendon 

 ■of the extensor metacarpi radialis, and is continued over it 

 by two tendinous slips, of which the posterior runs obliquely 

 to the elbow joint, like the ' passerine slip ' of many birds. 

 'The common tensor patagii muscle is usually very large, and 

 often completely covers the posterior deltoid [d. major). 

 Gabkod. dissected away the anterior thickened tendon of the 

 brevis in Deroptyus accipitrinus, and found it to arise from 

 a distinctly separate slip of the patagial muscle aj;tached to 

 clavicle. The tendon in question is inserted on to the lower 

 •externar humeral process, and may represent with its muscle. 



