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CT examination of the head of the Baikal seal (Phoca sibirica)

Published online by Cambridge University Press:  01 January 1999

HIDEKI ENDO ,
HIROYUKI SASAKI ,
YOSHIHIRO HAYASHI ,
EVAGENY A. PETROV ,
MASAO AMANO ,
NAOKI SUZUKI  and
NOBUYUKI MIYAZAKI
HIDEKI ENDO
Affiliation:
Department of Zoology, National Science Museum, Tokyo, Japan
HIROYUKI SASAKI
Affiliation:
Research Institute of North Pacific Fisheries, Hokkaido University, Hokkaido, Japan
YOSHIHIRO HAYASHI
Affiliation:
Department of Veterinary Anatomy, Faculty of Agriculture, University of Tokyo, Tokyo, Japan
EVAGENY A. PETROV
Affiliation:
Limnological Institute of the Siberian Division of the Academy of Sciences of Russia, Irkutsk, Russia
MASAO AMANO
Affiliation:
Otsuchi Marine Research Center, Ocean Research Institute, University of Tokyo, Iwate, Japan
NAOKI SUZUKI
Affiliation:
Department of Medical Engineering, Jikei University School of Medicine, Tokyo, Japan
NOBUYUKI MIYAZAKI
Affiliation:
Otsuchi Marine Research Center, Ocean Research Institute, University of Tokyo, Iwate, Japan
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Abstract

We carried out a computerised tomographic (CT) examination to elucidate the modifications in the head related to orbital enlargement in the Baikal seal. Transverse CT images showed that (1) the external frontal contours and the frontal sinuses are compressed medially and ventrally by the orbital enlargement; (2) the caudal part of the nasal cavity and nasopharynx are compacted ventrally; and (3) the cranial cavity is displaced caudally. The neurocranium is obviously separated from the facial part in the transverse plane at the caudal region of the orbit. The disposition of the mandible, zygomatic arch, temporal bone, and the masseter, temporal, digastric and pterygoid muscles is changed by the enlarged orbit in the 3-dimensional reorganisation of the head in this species. It is suggested that adaptation for the Lake Baikal environment primarily resulted in orbital enlargement, and that the altered orbital design may subsequently have influenced the form and function of the masticatory and respiratory system.

Keywords

Cranial osteologyeyeorbitskull
Type
Research Article
Information
The Journal of Anatomy , Volume 194 , Issue 1 , January 1999 , pp. 119 - 126
Copyright
© Anatomical Society of Great Britain and Ireland 1999

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