Abstract
The anatomy of the musculature of the wing and pectoral girdle of the
domestic fowl is redescribed.
The embryonic development of the musculature has been studied, and the
homologies of several muscles of the avian and reptilian shoulder regions have
been elucidated. As in other tetrapods which have been studied, the musculature
of the fore limb of the fowl first appears in the embryo as a pair of opposed
masses of condensed mesenchyme, one ventral and the other dorsal, forming in
the limb bud independently of the somites. These premuscle masses are lobed,
and their lobation enables the identification of the primordia of various muscle
groups at a very early stage of development, before the individual muscles have
differentiated.
The definitive muscles are formed by a process of splitting or cleavage of
the premuscle masses. The cleavages take place in an orderly sequence, which
closely resembles that which has been described in the lizard Lacerta, the turtle
Chrysemys, and the opossum Didelphys. It is concluded that the resemblances
in the lobate outlines of the premuscle masses and in the pattern of cleavages
in these vertebrates of different taxonomic groups are a reflection of the
phylogenetic history of the limb muscles. Thus the homologies of muscles in
tetrapods widely separated from one another taxonomically can be determined
more reliably by comparing their embryology than by comparing adults in which
the relationships of the muscles are obscured by adaptive changes.
Myological nomenclature is somewhat confused, owing to the difficulty of
determining homologies by studies confined to adult animals. A revision of the
names of avian wing muscles has therefore been carried out with the aim of
stabilizing the nomenclature for birds; in addition, some preliminary steps
towards a uniform nomenclature generally applicable to the muscles of all
tetrapods have been essayed, so far as comparative embryological data permit
conclusions to be drawn.
Subject
Animal Science and Zoology,Ecology, Evolution, Behavior and Systematics
Cited by
100 articles.
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