J Korean Neurosurg Soc.  2021 May;64(3):340-345. 10.3340/jkns.2021.0017.

A Tale of the Tail : A Comprehensive Understanding of the “Human Tail”

• Tojima S

• KMID: 2515489
• DOI: http://doi.org/10.3340/jkns.2021.0017

Abstract

Humans do not have tails; however, a congenital anomaly named “human tail” has been recognized since old times. In contrast with its impactful name, the anomaly itself is not fatal, and thus it has not been considered as a clinically serious symptom. However, many case reports suggested that retention of “the tail” is closely associated with spinal cord malformation and should be treated with care by neurosurgeons. Therefore, this review summarizes our knowledge regarding the anatomy, function, and development of the tail as a general structure in mammals. Learning the basic knowledge regarding tail anatomy and development would help clinicians to understand the “human tail” more concisely and to select more appropriate examinations or treatments in relation to this congenital anomaly.

Keyword

Congenital abnormality; Somites; Morphogenesis; Spine

Figure

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  Fig. 1. Anatomy of the tail. A : Caudal vertebrae. B : Basic anatomy of caudal musculatures in primates. 1 : M. abductor caudae medialis, 2 : M. abductor caudae lateralis, 3 : M. extensor caudae lateralis, 4 : M. extensor caudae medialis, 5 : M. iliocaudalis+M. pubocaudalis, 6 : M. ischiocaudalis, 7 : M. flexor caudae longus, 8 : M. flexor caudae brevis.

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  Fig. 2. Tail reduction process during human evolution. A common ancestor species of cercopithecoids and hominoids (Aegyptopithecus zeuxis) possessed a long tail. However, the common ancestral species of hominoids (Proconsul heseloni and Nacholapithecus kerioi) had lost their tails. Humans must also have lost their tails during this period, but no conclusive fossils have been found.

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  Fig. 3. Development of the tail. A : Gradient of gene expression during axial extension and termination. B : Somites in a human embryo. Somites are present up to the tip of the tail. NT : neural tube, RA : retinoic acid, CNH : chordoneural hinge, PSM : presomitic mesoderm.

Reference

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