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Possible "atavistic" structures in human aneuploids
Insights
Aneuploid neonates (trisomy 18 and 13) exhibit unusual supernumerary muscles, some absent in humans but common in primates. These may represent atavistic structures, offering insights into human evolutionary development.
Area of Science:
- Human Anatomy
- Developmental Biology
- Evolutionary Biology
Background:
- Aneuploidy, such as trisomy 18 and 13, can lead to developmental anomalies.
- Human anatomy occasionally presents variations, including supernumerary muscles.
Purpose of the Study:
- To document and analyze supernumerary muscles found in neonates with trisomy 18 and 13.
- To explore the potential evolutionary and developmental origins of these anatomical variations.
Main Methods:
- Detailed anatomical dissection of aneuploid neonates.
- Comparative analysis of identified muscles with primate anatomy.
- Review of embryological and evolutionary mechanisms.
Main Results:
- Identification of several supernumerary muscles (e.g., platysma occipitalis, rhomboidus occipitalis) not typically found in humans.
- Observation of muscle absence (e.g., palmaris longus) in some specimens.
- Presence of a linguofacial trunk in one specimen.
- Noted similarity of these muscles to those regularly found in monkeys and apes.
Conclusions:
- The supernumerary muscles in aneuploid neonates are suggested to be atavistic structures.
- These findings provide insights into primate muscle homologies and developmental pathways.
- Mechanisms for the development of these muscles in human aneuploids are proposed.
Abstract:
Comprehensive dissections of aneuploid (trisomy 18 and 13) neonates have revealed numerous supernumerary muscles that, although present in rare individuals, do not regularly occur in the human. These supernumerary muscles include: "platysma occipitalis," "rhomboideus occipitalis, "deltopectoral" complex, "latissimocondyloideus," "pectorodorsalis," "chondrohumeralis," and "peroneus digiti quinti"; a few muscles, e.g., palmaris longus and brevis are lacking altogether. One specimen exhibited a "linguofacial trunk" arising from the external carotid artery. The supernumerary muscles found in these aneuploid specimens are regularly found in monkeys and sometimes in the great apes. It is suggested that these supernumerary muscles may be "atavistic" structures. Problems in establishing homologies between these muscles among primates are discussed, and mechanisms leading to the development of these muscles in human aneuploids are proposed.