Viil A MANUAL OF THE BIRDS OF AUSTRALIA. 



are four in number, but only two of these are generally utilised, the heteroccelous 

 and opisthoccelous, and they vary rather erratically, so that they have little 

 primary importance. The shape of the coracoids, clavicles and scapulae 

 varies considerably and has been extensively quoted and appears to have 

 value in connection with the sternum. When the clavicles join, the combina- 

 tion is known as the furcula, and the presence or absence of such an item is 

 often important. The wing bones have not been much considered in connection 

 with taxonomy, but detailed study should allow good characters from the 

 development of these ; but here, as in the leg bones, adaptive features must 

 not be misunderstood. Thus, in the latter, the tarso-metatarsus has been 

 commonly cited when the development was purely adaptive and not of the 

 phylogenetic importance credited to it the study of the birds would have 

 explained this. 



The first and most commonly utilised item of the soft parts, generally 

 so called (not the soft parts external of the taxonomist), has been the formation 

 of the syrinx. The Passeriform birds have been divided into primary sections 

 by means of this organ, and it is certain that degradation has been mistaken 

 for lack of development. This is a matter which will be settled when the 

 new school of anatomists attack bird development from a scientific standpoint. 

 We will deal more particularly with this feature later on, as the modes of 

 syrinx development in the groups now being dealt with are of little importance, 

 the variation being inconstant. As above noted the development of the 

 carotid arteries was investigated by Nitzsch and elaborated by Garrod, who 

 practically proved that the feature was so inconstant as to be useless when 

 its confirmation would have been of value. The presence or absence of the 

 caeca was also studied with similar results, no satisfactory conclusions as to 

 its value being possible. Like conclusions attended similar research in 

 connection with the length of the intestines, the presence of the gall blader, 

 the size and position of the liver, etc., etc. Gadow considered the position of 

 the intestines as they are stowed away in the body, and Chalmers Mitchell 

 followed with a criticism of the methods of coiling of the intestinal canal. 

 From their results it appears that these follow definite lines and that, as 

 confirmatory evidence, they are probably quite as valuable a feature as any 

 other internal character. Garrod also investigated the muscles of the leg, 

 and, finding them variable as to their presence, endeavoured to influence 

 classification by their means. The mystic formula ABXY+ was invented 

 by him, and its variations are always cited in connection with bird grouping, 

 though its value is of little moment. The meaning of the letters had better 

 be explained here. A stands for the femoro-caudal muscle, B for the accessory 

 femoro-caudal, X for the semitendinosus, and Y for the accessory semi- 

 tendmosus, and the + sign for the presence of the ambiens muscle. The 

 -- minus is used if the latter be absent. The wing muscles have never been 

 given as much prominence, though they have just as much right and also 

 show variation, but their variation has not been tabulated as fully as that 

 of the leg muscles. Taken individually, as these characters have been, the 



