File:Bailey142.jpg: Difference between revisions

Fig. 142. Lateral dissection of head of human foetus

Showing derivatives of branchial arches in natural position.

Kollmann's Atlas.

In the mandibular process of the first visceral arch, the mandible develops as a bone which is partly of intramembranous and partly of intracartilaginous origin. In the first place a rod of cartilage, known as Meckel's cartilage, forms the core of the mandibular process and extends from the distal end of the process to the temporal region of the skull, where it passes between the tympanic bone and the periotic capsule and ends in the tympanic cavity of the ear (Fig. 136). During the sixth week of foetal life, intramembranous bone begins to develop in the mandibular process. In the region of the body of the mandible the bone encloses the cartilage, but in the region of the ramus and coronoid process the cartilage lies to the inner side of the bone. Development is further complicated by the appearance of cartilage in the region of the middle incisor teeth and on the coronoid and condyloid processes. These pieces of cartilage form independently of Meckel's cartilage and subsequently are replaced by the bone which constitutes the corresponding parts of the mandible. The part of Meckel's cartilage enclosed in the bone disappears; the part to the inner side of the ramus is transformed into the sphenomandibular ligament. (See Fig. 142.) In each half of the second branchial arch a rod of cartilage develops, which extends from the ventro-medial line to the region of the periotic capsule. The proximal end of this rod is then replaced by bone which fuses with the temporal bone and forms the styloid process. The distal (ventral) end is replaced by bone which forms the lesser horn of the hyoid bone. Between the styloid process and the lesser horn, the cartilage is transformed into the stylohyoid ligament (see Figs. 139 and 142). In each half of the third branchial arch a piece of cartilage develops and subsequently is replaced by bone to form the greater horn of the hyoid bone. The two horns become connected at their ventral ends by the body of the hyoid bone which is also a derivative of the third arch. Later the lesser horn fuses with the greater horn to bring about the adult condition (Fig. 142).

In the ventral parts of the fourth and fifth arches pieces of cartilage develop and form the skeletal elements, of the larynx. A more detailed account of these will be found under the head of the larynx.

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Reference

Bailey FR. and Miller AM. Text-Book of Embryology (1921) New York: William Wood and Co.

Cite this page: Hill, M.A. (2024, April 26) Embryology Bailey142.jpg. Retrieved from https://embryology.med.unsw.edu.au/embryology/index.php/File:Bailey142.jpg

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