112 MR. A. H. GARROD ON THE MUSCLES OF BIRDS. [Feb. 3, 



types of muscular arrangement in the thighs of birds, as far as the 

 four muscles uow under consideration are concerned. 



Each of the circles in the diagram is divided into two halves by 

 a vertical line, so that the names of all those birds which are found 

 to possess the ambiens muscle may be distinguished from those iu 

 which it is absent. The birds in which the ambiens is present are 

 placed in the left-hand semicircles ; those in which it is absent are 

 to be found in the right-hand semicircles. 



A few examples may illustrate the method of employing this table. 

 Taking the Musophagidce, for instance, they being found in the circle 

 A B. X Y evidently possess all the four muscles — the femoro-caudal, 

 the accessory femoro-caudal, the semitendinosus, and the accessory 

 semitendinosus ; and being on the left side, have also the ambiens. 

 The Strigidee being on the right side of the circle with the formula 

 A, possess only the femoro-caudal, the ambiens being also absent ; 

 and so on. Those birds whose names appear partly in both semi- 

 circles may or may not possess the ambiens muscle in their different 

 genera. 



Before going further it will be necessary to show what degree of 

 constancy is, as a rule, to be expected in the myology of birds. 

 Respecting this point my experience is that individuals of a species 

 agree precisely in their muscular arrangement. Many specimens of 

 a considerable number of species have passed through my hands, 

 and I have frequently dissected them one after another in order to 

 detect, if possible, any individual variations ; such, however, have 

 not been forthcoming. It is true that in a single specimen of CEdi- 

 cnemus grallarius the ambiens, instead of crossing the knee, ended on 

 the inuer side of the ligamentum patellae ; however, the muscle, 

 though imperfectly developed, was undoubtedly there. The only 

 other instance of an unexpected and abnormal individual structure 

 was the presence iu a specimen of Pomatorhinus temporalis, on one 

 side only, of an accessory femoro-caudal, which I have not once seen 

 in any other of at least 100 passerine birds that I have examined. 



From these observations it is evident that individuals of a species 

 all agree in the arrangement of the muscles of the thigh at least — 

 so much so that any peculiarity observed in a specimen dissected for 

 the first time may be taken to be characteristic of the species itself. 



The same remarks apply to the species of a genus. Of several 

 genera I have had the opportunity of dissecting many species, seven 

 of Bubo, six of Ardea and Columba, five of Buceros, Francolinus 

 and Ibis, four of Chrysotis, Brotogerys, and Geopelia, three of a large 

 number, and two of many more. In all these genera the myology 

 of the species does not vary, and its constancy is sufficient to justify 

 the suspicion that when there are muscular differences between the 

 species of an accepted genus, it is because genera have been com- 

 bined which ought to be kept distinct. Such is evidently the case 

 with Conurus, in which genus those without the red tail differ from 

 those possessing it (Pyrrhura), the ambiens muscle being present in 

 the former and absent in the latter. There are also other anatomical 

 differences between them. The genus Conurus, therefore, as at pre- 



