The Hindlimb Musculature of the White-Fronted Amazon (Amazona albifrons, Psittaciformes)

-The hindlimb musculature of six specimens of Amazona albifrons was dissected in order to (1) provide a detailed myological description, (2) provide a preliminary study and basis for a systematic analysis of the Psittaciformes, and (3) point out any myological peculiarities that might be associated with their unusually manipulative feet. Notable features include a peculiar positioning of M. extensor brevis digiti IV, a previously undescribed muscle to digit III, a peculiar arrangement of the short extensors of the hallux, and a branch of M. extensor digitorum longus to the hallux. These features are believed to be associated either with the zygodactyl digit configuration or the requirement of finer control over the individual digits. Received 15 March 1983, accepted 8 July 1983. THE order Psittaciformes includes about 332 living species. If only external characters are considered, it is a relatively homogeneous group. Hence, there has never been any confusion as to whether or not a species belonged to the order. The Psittaciformes is so morphologically distinct from other avian orders, however, that even comprehensive recent works (Sibley and Alquist 1972, Cracraft 1981) have failed to elucidate its systematic position. Relationships within the order are also uncertain. The fundamental argument has been over the reality of what appears to be a very uniform group. Using a variety of anatomical characters, researchers have proposed as few as one and as many as 11 families (Garrod 1874, Salvadori 1891, Mivart 1895, Thomson 1899, Mudge 1902, Glenny 1957, Brereton 1963, Holyoak 1973, Homberger 1980). Despite the invaluable anatomical information provided by these workers, the relationships within the Psittaciformes continue to be a matter of considerable confusion. There is a need for comprehensive studies using appropriate characters, along with a contemporary approach to analysis. Some of the more informative current avian phylogenies have been based on appendicular myology (Borecky 1977; Raikow 1977, 1978; Bentz 1979; Raikow et al. 1980; Sweirczewski and Raikow 1981; Maurer and Raikow 1981). A similar analysis of the Psittaciformes thus seems appropriate. The present, primarily descriptive, account is the first in a planned series of studies of the hindlimb musculature of the Psittaciformes. A comprehensive description of a parrot hindlimb has not been previously written. This study thus will not only be a first step toward a systematic analysis of the group but will provide a basis for future morphological comparisons with other avian orders. MATERIALS AND METHODS I dissected one hindlimb of each of six preserved specimens of Amazona albifrons under a stereomicroscope with a magnification of 6-25x . I used iodine stain (Bock and Shear 1972) to demonstrate small muscles clearly and to elucidate fiber architecture. Drawings were made with a camera lucida. Anatomical nomenclature is in accordance with the "Nomina Anatomica Avium" (Baumel et al. 1979). DESCRIPTION OF HINDLIMB MUSCLES M. iliotibialis cranialis (Figs. 1, 2: IC).-This strapshaped muscle arises by fleshy fibers from the aponeurosis covering the dorsal surface of the most caudal vertebra, from the cranial 6 mm of the dorsal crest of the synsacrum, and from the cranial 3 mm of the aponeurosis that covers M. iliotrochantericus caudalis. The muscle extends distally, defining the cranial border of the thigh. It narrows to about 4 mm to insert by fleshy fibers on the cranial cnemial crest of the tibiotarsus. In one specimen a few fibers insert on the aponeurosis of M. femorotibialis internus about 7 mm from the distal end of the femur. M. iliotibialis lateralis (Figs. 1, 2: IL).-Only a preacetabular portion is present. The sheet-like muscle originates by an aponeurosis that extends along the caudal one-half of the dorsal iliac crest to the femoral trochanter. The aponeurosis completely covers M. iliofemoralis externus and the caudal one-half of M. 74 The Auk 101: 74-92. January 1984 This content downloaded from 207.46.13.21 on Tue, 27 Sep 2016 04:04:22 UTC All use subject to http://about.jstor.org/terms January 1984] Parrot Hindlimb Musculature 75