EMBRYOLOGY OF FROG-Development of Notochord or Notogenesis in frog

The presumptive notochordal material is present in the roofoftlic archenteron as a longitudinal strip. It becomes separated from the adjacent mesoderm and underlying endoderrn. The cells arrange thcniselvcs to form a cylindrical rod called noroclmrd. In this stage, the notochord is attached to the underlying endoderm by a band of cells called hypochrirdal or sub-notochordal rod. It develops only in amphibian embryo and degenerates immediately. The notochord exceeds from the pituitary body of the brain to the end of the tail.At first  , the cells of notochord are closely packed but  later they fuse together and become vacuolated except  a layer of pe ripheral cells.
Later sheaths are formed around the notochord.There are mainly three sheaths a0Primary sheath is formed by superficial chordal cells.it is an elastic sheath of connective tissue. b. The secondary fibrous sheath is  formed by the chordal epithelium and c. The skeletogencus Sheath derived from the sclerotome.