Transcript
DEVELOPMENT OF TONGUE AND MANDIBLE..
DEVELOPMENT OF TONGUE.
Development of tongue starts in 4th month of intra-uterine life.
The tongue is composed of the body,which is the movable oral part and posterior base or pharyngeal part.
The tongue develops from tissue of 1st,2nd ,3rd, branchial arches as well as from occipital myotomes.
Tongue forms in the ventral floor of pharynx after arrival of hypoglossal muscle cells.
The body of tongue develops from three centrally placed elevation on the ventromedial aspects of first branchial arch.. 1. Tuberculum impar 2. Two adjacent elevation i.e. lateral lingual swelling.
The lingual lateral swellings are partially seperated from eachother by another swelling appear in the midline i.e. tuberculum impar.
Immediately behind tuberculum impar epithelium proliferates to form down growth from which thyroid gland develops,
The site of this is marked by depression called as foramena caecum… the foramena caecum marks the junction between anterior 2/3 and posterior 1/3 of the tongue.
The base of the tongue develops mainly from third branchial arch..
Another midline swelling is seen in relation to medial end of 2nd,3rd, and 4th arches.This swelling is hypobranchial eminence.
The eminence shows subdivision in the cranial part related to the 2nd and 3rd arches called as copula..caudal part related to 4th arch forms epiglottis.
The site of union of base and body of the tongue delinated body v-shaped groove called as sulcus terminalis.
ANTERIOR 2/3rd OF TONGUE.
The anterior 2/3rd of tongue is thus derived from mandibular arch.
It is covered by the epithelia of ectodermal origin.
Connective tissue component is derived from 1st arch mesenchyme.
POSTERIOR 1/3rd OF TONGUE.
It is formed from the cranial part of the hypobranchial eminence(copula).
At the time 2nd arch mesoderm burried below the surface,3rd arch mesoderm grows over it to fuse with mesoderm of 1st arch. Thus posterior 1/3rd of tongue is formed by 3rd arch mesoderm.
The posterior most part of the tongue is derived from the fourth arch.
The posterior 1/3rd of the tongue is covered by epithelia of endodermal origin.
NERVE SUPPLY
Anterior 2/3rd
Posterior 1/3rd
Posterior most part
SENSORY Lingual(post trematic branch of 1st arch)
Glossoph-aryngeal.
Internal la-ryngeal branch of vagus.
TASTE Chorda tympanic(pre-trematic branch of vagus.
Glossoph-aryngeal.
Internal la-ryngeal branch of vagus.
NERVE SUPPLY OF TONGUE.
MUSCULATURE OF TONGUE.
Muscles of tongue are derived from occipital myotomes.
DEVELOPMENT OF
MANDIBLE.
INTRODUCTION.
The mandible is largest ,strongest,and lowest bone in the face.
It has horizontal curved body and two broad rami,that ascends posteriorly.
The body of mandible supports the mandibular teeth with the alveolar process.
DEVELOPMENT..
All the bones of the upper face develop by intramembranous ossification most of them close to cartilage of nasal septum.
Mandible develops as intramembranous bone lateral to cartilage of mandibular arch.
The mandible forms from the tissue of first branchial arch.
The cartilage of 1st arch forms the lower jaw in primitive vertebrates.
The mandible makes it appearance as bilateral structure,in sixth week of fetal life.
Meckles cartilage extend as a solid hyaline cartilaginous rod .It is surrounded by fibrocellular capsule.
It extends from developing ear region to the midline fused mandibular process.
Cartilage of each side are seperated by thin band of mesenchyme.
In 6th week on lateral aspect of mesenchyme ,a condensation of mesenchyme occur.
This condensation occur at an angle which is formed by the division of inferior alveolar nerve into incisive and mental branches.
In 7th week this condensation undergoes intramembranous ossification.This forms 1st bone of mandible.
Only small part of meckels cartilage undergoes ossification .Greater part of meckles cartilage get disappear without contribution to the formation of mandible.
From this centre of ossification bone formation spreads anterior to the midline.
It spread medially and posterocranially to form body and ramus,first below and than around the inferior alveolar nerve and incisive branch.
It than spreads upward initially forming a trough later crypts for developing teeth.
This trough consist of lateral and medial plates that unite beneath the incisor nerve.
Trough extends to the midline where it comes into close approximation with a similar trough formed in adjoining mandibular process.
Trough is soon converted into canal as bone forms over the nerve joining the lateral and medial plate.
A backward extension of ossification along the lateral aspects of meckels cartilage forms gutter,this gutter later converted into canal.
This backward extension of ossification proceed in a condensed mesenchyme to a point where mandible nerves divides into inferior alveolar nerve and lingual nerve.
From bony canal medial and lateral alveolar plates of bone develop into relation to forming tooth germ so that they occupy the secondary trough of bone.
This trough is partitioned and thus teeth come to occupy individual compartment.
These compartment are enclosed by the growth of bone over the tooth germ.
Thus body of mandible is formed…
Ramus of mandible.The ramus of mandible develops by a rapid spread of ossification posteriorly into the mesenchyme of the first arch tuning away from meckles cartilage.
This point of divergence is marked by lingula in adult mandible.
It is point at which inferior alveolar nerve enters the body of mandible.
Thus by 10th week rudimentary mandible is almost entirely formed by membranous ossification.
Thus ramus of mandible is formed…
AGE CHANGES IN MANDIBLE.
IN INFANTS AND IN CHILDREN
Two halve of mandible fuse during the 1st year of life.
At birth mental foramen open below the socket of two deciduous molar teeth near the lower border.
The mandibular canal runs near the lower border.
The angle is obtuse it is 140
The coronoid process is large projects upward above the level of condyle.
IN ADULT:
Mental foramena opens midway between upper and lower border.
Mandibular canal runs parallel with the mylohyoid line.
The angle reduce to 110-120
IN OLD AGE:
Height of body is markedly reduces.
Mental foramen and mandibular canal are close to alveolar border.
The angle again become obtuse.
Submitted by: preeti dagdiya intern 06
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