Journal
JOURNAL OF MORPHOLOGY
Volume 270, Issue 9, Pages 1069-1083Publisher
WILEY-BLACKWELL
DOI: 10.1002/jmor.10743
Keywords
head cavities; development; segmentation; epigenesist; crocodile
Categories
Funding
- Academy of Sciences of the Czech Republic [KJB6111301]
- NATO Fellowship Programme and Center for Higher Education Studies, Czech Republic [MK2003-13]
- Charles University, Czech Republic [122/2003-B]
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Three consecutive pairs of head cavities (premandibular, mandibular, and hyoid) found in elasmobranchs have been considered as remnants of preotic 'head' somites-serial homologues of the myotomic compartments of trunk somites that give rise to the extraoccular musculature. Here, we study a more derived vertebrate, and show that cavitation is more complex in the head of Crocodylus niloticus, than just the occurrence of three pairs of cavities. Apart from the premandibular cavities, paired satellite microcavities, and unpaired extrapremandibular microcavities are recognized in the prechordal region as well. We observed that several developmental phenomena occur at the same time as the formation of the head cavities (premandibular, satellite, extrapremandibular, mandibular, and hyoid) appear temporarily in the crocodile embryo. These are 1) rapid growth of the optic stalk and inflation of the optic vesicle; 2) release of the intimate topographical relationships between the neural tube, notochord and oral gut; 3) tendency of the prechordal mesenchyme to follow the curvature of the forebrain; and 4) proliferation of the prechordal mesenchyme. On the basis of volumetric characters, only the hyoid cavity and hyoid condensation is comparable to the trunk somitocoel and somite, respectively. J. Morphol. 270:1069-1083, 2009. (C) 2009 Wiley-Liss, Inc.
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