| OCR Text |
Show 1874.] MR. A. H. GARROD ON THE MUSCLES OF BIRDS. Ill 1. O n certain Muscles of Birds and their Value in Classification. Part II. By A. H . G T A R R O D , B.A., Fellow of St. John's College, Cambridge, Prosector to the Society. [Eeceived January 6, 1873]. (Plate XVII.) The facts contained in the former part of this communication (P. Z. S. 1873, p. 626) being in an expanded form, it is not easy to appreciate their full significance at a glance, nor without considerable difficulty. To obviate this inconvenience I have constructed the following table, which is so arranged that by a very simple method, it is possible to tell without further reference which of the five muscles-the ambiens, the femoro-caudal, the accessory femoro-caudal, the semitendinosus, and the accessory semitendinosus-are present or absent. To obtain this result the names of the muscles themselves have been omitted, and single letters of the alphabet used in their stead. The femoro-caudal is represented by A The accessory femoro-caudal B The semitendinosus X The accessory semitendinosus Y When these four muscles are present in a bird the formula A B. X Y expresses the fact; when any one is absent, that such is the case is indicated by the omission of the letter representing it. Thus the formula A. X Y indicates that the accessory femoro-caudal muscle only is absent; A B. X that the accessory semitendinosus is missing ; A. X that the femoro-caudal and semitendinosus only are to be found ; and A that the femoro-caudal alone is present. These formulae may be termed myological formulae. No bird is known in which all these four muscles are deficient. In the accompanying diagram (Plate XVII.) all those birds which have the same myological formula are included together in one circle ; and the circles are so placed in relation to one another that, if they were drawn on the surface of a sphere, there would be only a single operation of addition or subtraction necessary to move from any one to any of its immediate neighbours. Of the four letters A, B, X, and Y the following are the sixteen possible combinations. AB.XY AB B.XT XT AB.X A.X B.X X AB.Y A. Y B. Y Y A. XT A B O Those printed in italics are those which, if considered as myological formulae on the nomenclature above given, have been found amongst birds ; in other words, there are eight different |
