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Meckel's cartilage is a piece of cartilage from which the mandibles (lower jaws) of vertebrates evolved. Originally it was the lower of two cartilages which supported the first branchial arch in early fish. Then it grew longer and stronger, and acquired muscles capable of closing the developing jaw. [1]
In contrast to the Meckel's cartilage of the first pharyngeal arch it does not constitute a continuous element, and instead is composed of two distinct cartilaginous segments joined by a faint layer of mesenchyme. [15]
The theory of recapitulation, also called the biogenetic law or embryological parallelism—often expressed using Ernst Haeckel's phrase "ontogeny recapitulates phylogeny"—is a historical hypothesis that the development of the embryo of an animal, from fertilization to gestation or hatching (), goes through stages resembling or representing successive adult stages in the evolution of the ...
The number of vertebrae in a region can vary but overall the number remains the same. In a human spinal column, there are normally 33 vertebrae. [3] The upper 24 pre-sacral vertebrae are articulating and separated from each other by intervertebral discs, and the lower nine are fused in adults, five in the sacrum and four in the coccyx, or tailbone.
Continuous with the dorsal end of the first pharyngeal arch, and growing forward from its cephalic border, is a triangular process, the maxillary prominence (or maxillary process), the ventral extremity of which is separated from the mandibular arch by a ">"-shaped notch.
Human embryo at the end of week 4 with somite development. In the developing vertebrate embryo , somites split to form dermatomes, skeletal muscle (myotomes), tendons and cartilage (syndetomes) [ 9 ] and bone (sclerotomes).
The face and neck development of the human embryo refers to the development of the structures from the third to eighth week that give rise to the future head and neck.They consist of three layers, the ectoderm, mesoderm and endoderm, which form the mesenchyme (derived form the lateral plate mesoderm and paraxial mesoderm), neural crest and neural placodes (from the ectoderm). [1]
In some fishes, the palatoquadrate is the dorsal component of the mandibular arch, the ventral one being Meckel's cartilage. The palatoquadrate forms from splanchnocranium in various chordates including placoderms and acanthodians .