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Amphibian development
(10 mm larvae; sagittal sections)
Faculty of Biological Science and Technology
Zoology and Botanical department
Practical embryology
By: Shirin Kashfi
Ph.D in Animal Development
Stages in the Normal Development of Rana pipiens
Stages in the Normal Development of Rana pipiens
Stages in the Normal Development of Rana pipiens
Stages in the Normal Development of Rana pipiens
ventral surface
stage 24, 240 hpf, 1o mm Head and trunk are expanded Tail is long and muscles are
segmented Brain is more developed Optic cup obviously
differentiated to retianl pigmented epithelium (RPE) and neural retina
Mouth has been opened and gut differentiated further
Horny jaws, teeth and papilla are seen in mouth
operculum closed on right One pair pigmented oral
suckers are seen in ventral surface of head
retina
lens
retinal pigmented epithelium (RPE)
auditory vesicle
pronephric ducts
operculum
external gills
gut
liver
RPE
Rho.
mouth
Mes..
notochord
heart
gut
lung
pharynx
forbrain
rectum
spinal ganglions
spinal cord
Mes.: mesencephalon; Rho.: rhombencephalon
thyroid
ventral tail fin
dorsal tail fin
myomere
notochord
proctodeum
liver
mesonephric duct
Embryonic pharynx
pharyngeal (branchial) apparature is made up of clefts, arches and pouches
Branchial apparatus (pharyngeal apparatus)
branchial clefts (branchial grooves)
derived from ectoderm located between the arches
branchial arches
derived from mesoderm (muscles, arteries) and neural crest cells (bones,
cartilage)
each arch is associated with a cranial nerve
branchial pouches
derived from endoderm which line the foregut
The pharyngeal arches surround the ventrolateral pharynx in the early embryo. Between the bodies of adjacent aches are a pharyngeal cleft or furrow on the outside of the body, and a pharyngeal pouch on the inside. Also, before the tongue forms in the floor of the pharynx there is a centrally located depression called the foramen cecum. The tissues of the foramen cecum eventually migrate to the neck and form the thyroid gland
The eustachian tube and middle ear cavity are derived from the space of pharyngeal pouch I. The outer ear canal develops from the first cleft. The tympanic membrane is developed from tissues that separate the two cavities.
Other soft organs are derived from the endodermal lining tissues of pharyngeal pouches 2-6. The tonsils which form from the wall of the second pouch remain in the pharynx, but the other tissues migrate in a fashion similar to the thyroid. Masses of tissues from the anterior parts of the pouches 3 and 4 will form the parathyroid tissues. Tissues from the posterior parts of pouch 3 and 4 migrate to the mediastinum and form the thymus. Special calcitonin producing cells, sometimes referred to as the untimobranchial tissue, originate in the wall of the 5th pouch and become intermingled with thyroid tissues in humans.