Abstract
In order to determine the normal stages of formation in the sequence of ossification of the cranium of Podocnemis expansa in its various stages of development, embryos were collected starting on the 18th day of natural incubation and were subjected to bone diaphanization and staining. In the neurocranium, the basisphenoid and basioccipital bones present ossification centers in stage 19, the supraoccipital and opisthotic in stage 20, the exoccipital in stage 21, and lastly the prooptic in stage 24. Dermatocranium: the squamosal, pterygoid and maxilla are the first elements to begin the ossification process, which occurs in stage 16. However, ossification centers begin to appear in stage 17 in most of these bone elements, i.e., the frontal, jugal, postorbital, parietal, premaxilla and prefrontal, followed by the palatine and quadratojugal in stage 19 and lastly by the vomer in stage 25. The quadrate bone of the splanchnocranium ossifies in stage 23. The mandible and hyoid apparatus, the dentary, coronoid and supra-angular, show ossification centers in stage 16 and the branchial horn I in stage 17. The sequence and synchronization of ossification in P. expansa show similarities as well as differences when compared with other species of Testudines.
Highlights
The skeleton of vertebrates is composed of cartilage and bone and is the product of cells from three distinct embryonic lines
Sixty-two embryos of Podocnemis expansa (Testudines, Podocnemididae) were collected during the spawning period of 2005 and 2006, in the area of reproduction protected by the RAN – Center for Reptile and Amphibian Conservation and Management on the beaches of the Araguaia river in Goiás State, Brazil, in the region called Remansão (13o 20' 38.7" S and 50o 38' 05.7" W), under permit number 117/2005-IBAMA/RAN
The specimens were subjected to diaphanization by KOH and staining of bones with alizarin red S and of cartilage with alcian blue, according to the method of Davis and Gore (1936) and Dingerkus and Uhler’s (1977) modified method, at the Wild Animal Research Laboratory (LAPAS) of the Federal University of Uberlândia (UFU) Faculty of Veterinary Medicine
Summary
The skeleton of vertebrates is composed of cartilage and bone and is the product of cells from three distinct embryonic lines. The cranium is composed of neural crest cells (OLSEN et al, 2000; CLARK et al, 2001). The cells of this line migrate to where the skeletal elements will develop, forming characteristic condensations of mesenchymal cells and differentiating into osteoblasts or chondrocytes. Biological Sciences into osteoblasts directly produces membrane bones, while in others differentiation into chondrocytes produces cartilage models of future bones. These cartilage models are later replaced by bone through endochondral ossification (OLSEN et al, 2000)
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