1874.] MR. A. H. GARROD ON THE MUSCI.ES OF BIRDS. 113 



sent generally defined, is too extensive, and from it must be sepa- 

 rated off the genus Pyrrhura of Bonaparte. 



In Euplocamus there is an apparent slight exception to the 

 uniformity in generic myology. In some species, as E. erythroph- 

 thalmus, E. albocristatus, and E. horsfieldii, the femoro-caudal is 

 present, though very small indeed ; in a specimen of E. vieilloti, 

 however, it could not be found at all. This tendency to the entire 

 disappearance of an almost obsolete muscle, however, can have but 

 little weight in generalizations of the character under consideration. 



Ascending to the next zoological grade, in the families of birds 

 there may be myological differences, though in some, such as the 

 Anatidae, the Accipitres proper, the Strigidae, and most of the smaller 

 families, none have yet been found. The femoro-caudal is the muscle 

 which seems to be the most susceptible of variation. Amongst the 

 Cathartidae it is present in Cathartes and absent in Sarcorhamphus 

 and Gyparchus. Amongst the Gallinae it is absent in Pavo and 

 Meleagris, very small or absent as above mentioned in Euplocamus, 

 and well developed in Gallus and Argus. The various genera of 

 Columbse and Psittaci may or may not possess the ambiens, as is the 

 case with Conurus and Pyrrhura mentioned above. Amongst the 

 Cuculidae, the Ground-Cuckoos {Centropus, Guira, Phoenicophaus) 

 differ from Cuculus and its allies in having the accessory femoro- 

 caudal developed, whilst it is absent in the latter, their respective 

 formulae being A B. X Y and A. X Y. This peculiarity, when added 

 to those in the pterylosis, justifies the division of the family into two 

 subfamilies, which may be termed the Centropodince and the Cuculince. 

 In the same way the Pici differ among themselves in possessing or 

 being deficient of the accessory semitendinosus, Picus being one of 

 the latter, whilst Gecinus, Leuconerpes, &c. are of the former. 



It may be inferred from the above statements that in the families 

 of birds, though there may be myological differences amongst the 

 genera, these differences are never more considerable than such as 

 consist of the absence of one muscle from the typical arrangement of 

 the family, or, in other words, from the modification of one element 

 of the typical formula. When, therefore, it is found that under any 

 accepted arrangement there are subfamilies differing from one 

 another by more than a single muscular peculiarity, there is reason 

 to expect that these subfamilies would be further separated in a 

 natural arrangement. The Accipitres furnish an example ; the 

 myological formulae of its subdivisions are subjoined, + and — in- 

 dicating the presence or absence of the ambiens muscle : — 



Falconidee A + 



Vulturidee A + 



Cathartidae A. X Y+ or X Y+ 



Strigidae A — 



Serpentariidce B.XY + . 



This table makes it evident that the Falconidee and Vulturidae 

 are widely separated from the Cathartidae and the Serpentariidce, 

 and that it is perfectly impossible to unite in any intimate way these 



Proc. Zool. Soc— 1874, No. VIII. 8 



