Muscles of the Avian Hip and Thigh

Abstract

AN increase of interest in the myology of birds is apparent. The more recent papers on the subject, however, concern themselves with a comparison of the muscles of different avian groups, and pay but slight attention to homologics. There have been few contributions toward an understanding of the latter, and most authors refer to Gadow's work of forty-six years ago (in Bronn's 'Klassen und Ordnungen des Tier-Reichs,' 1891). Exceptional in this respect have been two papers of Romer, one (Jour. Morph., 43: 347-385, 1927) on the development of the muscle groups of the pelvic limb of the chick, and another (Bull. Amer. Mus. Nat. Hist., 48: 533-552, 1923) that considers the muscles of birds rather incidentally with those of (chiefly) Alligator. Hudson's paper ('Studies on the muscles of the pelvic appendage in birds,' Amer. Midland Nat., 18: 1-108, 1937) is a notable contribution to our knowledge of interordinal variations of the muscles of the pelvic limb in birds, but unfortunately for the morphological myologist, he failed to consider the innervations, and hence his paper is of little use from this aspect. Recently I have completed a study of the muscles of hip and thigh of all vertebrate classes, and the results of this, as bearing on mammalian homol-ogies, are contained in a paper now in press, 'Morphogenesis of the architecture of hip and thigh.' This contains only minor references to the conditions in birds, however, for Aves are usually considered, whether rightly or wrongly, as being too specialized to have much bearing on the morpho-genesis of other vertebrate classes. Accordingly it appears advisable to offer a separate paper dealing with birds. As the topographical royology of birds is well known, descriptions are reduced to the minimum compatible with a clear presentation. Gallus gallus was chosen as the subject for discussion , since it is a type relatively unspeeialized and is easily procurable. It is deemed unnecessary to repeat the discussions offered in my paper referred to above; hence the two papers should be used together. A few pertinent points regarding the osteology are mentioned for a better understanding of the discussions. The posture of birds varies considerably. In some, as penguins, loons, grebes, the position of the trunk, when on land, is largely vertical, in order to bring the center of gravity above the aeetabula, and may be likened to that of man. In other sorts the body is inclined at an angle when at rest or while walking, but in many terrestrial types (as Gallus) the body is carried with its long axis almost parallel to the ground, a position assumed by no bipedal mammal nor extinct bipedal reptile without a heavy tail for