Dorsal notch of foramen magnum due to incomplete ossification of supraoccipital bone in dogs

Authors

  • A. G. Watson,

    1. Department of Anatomy, New York State College of Veterinary Medicine, Cornell University, Ithaca, New York 14853, USA
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    • *Department of Physiological Sciences, College of Veterinary Medicine, Oklahoma State University, Stillwater, Oklahoma 74078, USA.

  • A. de Lahunta,

    1. Department of Anatomy, New York State College of Veterinary Medicine, Cornell University, Ithaca, New York 14853, USA
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  • H. E. Evans

    1. Department of Anatomy, New York State College of Veterinary Medicine, Cornell University, Ithaca, New York 14853, USA
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ABSTRACT

The shape of the foramen magnum and the variation in the ossification pattern of the supra-occipital bone were studied in 48 skulls, including 12 from neonatal and 33 from immature and mature beagles of known age. The shape varied markedly, and a dorsal notch, dorsomedial to the nuchal tubercles and present in over half of the beagles, developed as a result of incomplete ossification of the ventromedial part of the supra-occipital bone. In a pomeranian and a chihuahua a membrane of dure mater and connective tissue, which covered the prominent dorsal notch, prevented prolapse of the brain. The spinal cord passed through a smaller oval opening in the ventral half of the foramen magnum. As there was no apparent impairment of function or anomalies associated with the dorsal notch and since a prominent dorsal notch was common in small breeds with brachycephalic skulls, it was concluded that the dorsal notch is a variation in the normal morphological pattern.

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