Prenatal and postnatal development of the cervical portion of the spine in the short-finned pilot whale Globicephala macrorhyncha

Authors

  • John A. Ogden,

    1. The Section of Orthopaedic Surgery, The Skeletal Growth and Development Study Unit, and the Marine Mammal Stranding Study Center, Yale University School of Medicine, New Haven, Connecticut 06510
    Current affiliation:
    1. Professor and Chief of Orthopaedics, Yale University School of Medicine, 333 Cedar Street, New Haven, Connecticut 06510
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  • Kendrick E. Lee,

    1. The Section of Orthopaedic Surgery, The Skeletal Growth and Development Study Unit, and the Marine Mammal Stranding Study Center, Yale University School of Medicine, New Haven, Connecticut 06510
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  • Gerald J. Conlogue,

    1. The Section of Orthopaedic Surgery, The Skeletal Growth and Development Study Unit, and the Marine Mammal Stranding Study Center, Yale University School of Medicine, New Haven, Connecticut 06510
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  • James S. Barnett

    1. The Section of Orthopaedic Surgery, The Skeletal Growth and Development Study Unit, and the Marine Mammal Stranding Study Center, Yale University School of Medicine, New Haven, Connecticut 06510
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Abstract

Fusion of the cervical spine in Globicephala macrorhyncha is a prenatal rather than postnatal phenomenon which encompasses all cervical vertebra. This results in a relatively short, nonarticulated, composite cervical spine in this particular species. Cervicothoracic spine segments removed from fetuses demonstrated complete fusion of all cervical vertebra commencing during early prenatal development. C1 and C2 initially developed as a composite central cartilaginous unit, although laterally there was some separation through rudimentary interzone formation. However, C3 through C7 formed individual cartilaginous centra which were divided from each other by thin, well-demarcated interzones, but without the formation of intervertebral discs (which were concomitantly evident dividing the thoracic, lumbar, and caudal vertebra, and were also present between the seventh cervical and first thoracic vertebra, although this was a very rudimentary intervertebral region). The first primary ossification center appeared in C2. Subsequently, primary ossification occurred in C7, and finally in C2 through C6, with ossification progressing in a craniocaudal fashion in these four vertebra. The centra ossification centers then progressively coalesced in the midline, from C2 to C7, in a craniocaudal sequence. This entire chondroosseous fusion process was completed during early gestation (probably less than 2 to 3 months of prenatal development), so that a composite “single” cervical vertebra developed that characterizes this species at birth and throughout postnatal development. Postnatally, ossification spreads laterally within each centrum, and also progressively removes the vestiges of the intervertebral material. C7 also develops a secondary ossification center, but only in the caudal region. The cranial end of C7 and the remainder of the cervical vertebra do not form secondary centers. An extensive fibrocartilaginous/hyaline cartilage bridge remains between C1 and C2, even after closure of the vertebral physes. Undoubtedly, this allows continued growth in C1 and C2, which become the dominant portion of the cervical unitary vertebra. Eventually, even this synchondrosis will disappear to form a completely osseous cervical mass.

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