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

Sh.kashfi@staf.ui.ac.ir

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.