Handout Embryology

Topics: Developmental biology, Embryology, Cranial nerves Pages: 4 (714 words) Published: December 12, 2010

Click on pictures for an enlarged view of the graphic.
Refer to Picture 1, 2 and 3
(from: James K Avery: Essentials of Oral Histology and Embryology - A Clinical Approach, Mosby Year Book)
Picture 1|
Picture 2|
Picture 3|
The branchial (=Gr gill) apparatus comprises an early structure during embryologic development. It is associated with the formation of the head and neck. It consists of the branchial arches, the pharyngeal pouches, the branchial clefts or grooves and the branchial membranes (not pictured). A four-week-old embryo features four visible branchial arches separated by branchial grooves. They are numbered craniocaudally. A fifth and a 6th are also present but are very small. A primitive mouth appears as a small depression referred to as stomatodeum (stomodeum). The oropharyngeal (buccopharyngeal) membrane separates the stomatodeum from the primitive pharynx (cranial part of the foregut). This membrane ruptures at 24 to 26 days and communication with the amniotic cavity is established. Identify Rathke's pouch in Picture 3 and review your notes on the subject. BRANCHIAL ARCHES

Refer to Picture 4
(from: William J. Larsen: Human Embryology, Churchill Livingstone)

Picture 4
1st branchial arch (mandibular arch) gives rise to the maxillary and the mandibular prominences. Identify the 1st branchial arch cartilage or Meckel's cartilage. It does not form the mandible.
Indicates the position of the future mandible.
The mandible develops by intramembranous ossification.
The malleus and the incus develop by endochondral ossification of the dorsal aspect of this cartilage. Innervation: V cranial nerve
2nd branchial arch cartilage (Reichert's cartilage)
Forms the stapes, styloid process, and superior hyoid bone. 3rd branchial arch forms the lower aspect of the hyoid. 4th and 6th branchial arch form the thyroid and cartilages of the larynx. PHARYNGEAL POUCHES

Refer to Picture 1
(from: James K Avery: Essentials of Oral...
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