Vili 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 scapule 
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 
oftenimportant. 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 
ceca 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., ete. 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- 
tendinosus, 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 vartation has not been tabulated as fully as that 
of the leg muscles. Taken individually, as these characters have been, the 
