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  • Title: [Evolutionary dispositon of the thoracic extremities and the fate of the coracoids and scapulae in vertebrates].
    Author: Manziĭ SF, Moroz VF.
    Journal: Arkh Anat Gistol Embriol; 1981 Jul; 81(7):20-8. PubMed ID: 7295049.
    Abstract:
    It is of general opinion that the mammalian coracoid bone reduced during the evolutional process and remained as a small tubercle on the distal part of the scapula. The cause of the caracoid bone reduction is supposed to result from certain changes in position of the free thoracic extremity from the segmental (as in reptiles) plane into the sagittal one, while the position of the shoulder girdle remained unchanged. However, this view does not coincide to the paleontological data which state that already in the Dinosauria and Theriodontia the thoracic extremities were situated in the parasagittal plane and, nevertheless their caracoids were well developed. There is also no agreement with numerous embryological, comparative-anatomical and electromyographic data concerning the osseous-muscular system of the thoracic extremities and the evolutional transformation of the brachial plexus. Owing to these data, it is possible to suggest that in the process of the mammalian evolution, the thoracic extremity together with the shoulder girdle made a turn around its longitudinal axis and, as a consequence, the caracoid with its musculature, moved from its abdominal position forward and upward on the lateral and spinal surface, and the scapula, correspondingly, in the caudoventral direction and gradually reduced.
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