Page 113. 
210 ON CERTAIN MUSCLES OF BIRDS. 
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 combined 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 present generally 
defined, is too extensive, and from it must be separated off the genus 
Pyrrhura of Bonaparte. 
In Luplocamus there is an apparent slight exception to the uni- 
formity in generic myology. In some species, as H. erythrophthalmus, . 
EF. albocristatus, and H. horsfieldit, the femoro-caudal is present, 
though very small indeed; in a specimen of HF. 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 
Anatide, the Accipitres proper, the Strigide, 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 
Cathartide it is present in Cathartes and absent in Sarcorhamphus and 
Gyparchus. Amongst the Galline it is absent in Pavo and Meleagris, 
very small or absent as above mentioned in Huplocamus, and well 
developed in Gallus and Argus. The various genera of Columbee and 
Psittaci may or may not possess the ambiens, as is the case with 
Conurus and Pyrrhuwra mentioned above. Amongst the Cuculide, the 
Ground-Cuckoos (Centropus, Guira, Phenicophaes) differ from Cuculus 
and its allies in having the accessory femoro-caudal developed, whilst 
it is absent in the latter, their respective formule being A B. X Y and 
A. XY. This peculiarity, when added to those in the pterylosis, 
justifies the division of the family into two subfamilies, which may be 
termed the Centropodine and the Cuculine. 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 
