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Show 1874.J MR. A. H. GARROD ON THE MUSCLES OF BIRDS. 113 sent generally defined, is too extensive, and from it must be separated 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 Strigidse, 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 Cathartidse 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 Columbae 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 Centropodina and the Cuculinte. 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 - indicating the presence or absence of the ambiens muscle :- Falconida A-f Vulturidce A + Cathartida A. X Y + or X Y+ Strigida A - Serpentariida B. X Y + . This table makes it evident that the Falconida and Vulturida are widely separated from the Cathartida and the Serpentariida, and that it is perfectly impossible to unite in any intimate way these P R O C Z O O L . Soc-1874, No. VIII. 8 |