At the end of 4th week The frontonasal prominence forms upper border of stomatodeum. Maxillary laterally. Derivatives of Facial Components The frontonasal prominence forms the: Forehead and the bridge of the nose Frontal and nasal bones. The maxillary prominences form the: Upper cheek regions and most of the upper lip Maxilla, zygomatic bone, secondary palate. The mandibular processes fuse and form the: Chin, lower lip, and lower cheek regions Mandible The lateral nasal prominences form the ala of the nose.
Face consists of a few primordial tissue masses partially surrounding the future oral region. The oral cavity stomodeum is an ectodermal depression separated from the foregut by the Oral plate formed of ectoderm on one side and endoderm on the other. The face is dominated by the frontal prominence of the overhanging forebrain. Laterally, the maxillary processes of the 1st branchial arch are visible.
On either side of the frontal prominence are horseshoe-shaped elevations are found around the nasal placodes. Medial limbs are nasomedial processes b. Lateral limbs are nasolateral processes 2. Growing toward midline are the maxillary processes, approaching mandibular arches and merging with them at the angle of the mouth.
Maxillary processes grow to crowd the nasal processes closer together. Nasomedial processes grow quickly, pushing the frontal prominence , then fuse with the maxillary processes to complete the arch of the upper jaw.
Nasomedial tissues give rise to philtrum. The single frontonasal prominence ventral to the forebrain The paired maxillary prominences develop from the cranial part of first branchial arch The paired mandibular prominences develop from the caudal part of first branchial arch Lateral view. Simultaneously they grow in a medial direction thereby compressing the medial nasal prominences toward the midline. Initially the maxillary and the lateral nasal prominences are separated by a deep furrow ,the nasolacrimal groove.
The nasolacrimal duct then runs from the medial corner of the eye to the inferior meatus of the nasal cavity. The maxillary prominence then enlarge to form the cheek and maxillae. The first structure to develop in the region of the lower jaw is the mandibular division of the trigeminal nerve.
The prior presence of the nerve has been postulated as requisite for inducing osteogenesis by the production of neurotropic hormones. Single ossification centre for each half of the mandible arises in the 6th week i. Ossification begins below and around the Inferior Alveolar Nerve and its Incisive branch and upwards to form a trough for the developing teeth.
Spread of intramembranous ossification dorsally and ventrally forms the body and the Ramus of the mandible. The shape and size of he fetal mandible undergo considerable transformation during its growth and development. The ascending ramus of the neonatal mandible is low and wide ;the coronoid process is relatively large and projects well above the condyle ;the body is merely an open shell containing the buds of the deciduous teeth. The main sites of postnatal mandibular growth are at the condylar cartilages ,the posterior borders of the ramii and the alveolar ridges.
By the end of 4th week, bilateral oval-shaped ectodermal thickenings called nasal placodes appear on each side of the lower part of the frontonasal prominence Nasal placodes are primordia of the nose and nasal cavities. Mesenchymal cells proliferate at the margin of the placodes and produce horse-shoe shaped swellings around these.
The sides of these swellings are called medial and lateral nasal prominences The placodes now lie in the floor of a depression called nasal pits.
With the formation of the medial and lateral nasal prominences, the nasal placodes lie in the floor of depressions called the nasal pits By the end of 6th week, nasal pits deepen and form nasal sacs.
Initially the nasal sacs are separated from the oral cavity by oronasal membrane. The oronasal membrane ruptures by the 6th week, communicating the primitive nasal cavities with the oral cavity.
These communications are called the primitive choana and are located posterior to the primary palate. After the development of the secondary palate, the choana change their position and become located at the junction of nasal cavity and the pharynx. The nasal septum develops as a downgrowth from the internal parts of merged medial nasal prominences. The superior, middle and inferior conchae develop on the lateral wall of each nasal cavity The ectodermal epithelium in the roof of each nasal cavity becomes specialized as the olfactory epithelium.
The olfactory cells of the olfactory epithelium give origin to olfactory nerve fibers that grow into the olfactory bulb. Eye placode 2. Nasal placode 3. Oronasal membrane 4. Nasal cavity 5. Primary palate 7. Secondary palate. Intermaxillary Segment: As a result of medial growth of the maxillary prominences ,the two medial nasal prominences merge not only at the surface but also at a deeper level.
The structure formed by the two merged prominences is called as the intermaxillary segment. It is composed of : A Labial component which forms the philtrum of the upper lip. B Upper jaw component which carries the four incisor teeth.
C Palatal component-which forms the triangular primary palate. The medial nasal swellings enlarge, grow medially and merge with each other in the midline to form the intermaxillary segment. Begins at the end of the 5th week Gets completed by the end of the 12th week The most critical period for the development of palate is from the end of 6th week to the beginning of 9th week.
The Primary Palate Begins to develop: Early in the 6th week From the deep part of the intermaxillary segment, as median palatine process. Lies behind the premaxillary part of the maxilla Fuses with the developing secondary palate. The primary palate represents only a small part lying anterior to the incisive fossa, of the adult hard palate Primary palate. The Secondary Palate Is the primordia of hard and soft palate posterior to the incisive fossa Begins to develop: Early in the 6th week From the internal aspect of the maxillary processes, as lateral palatine process.
In the beginning, the lateral palatine processes project inferomedially on each side of the tongue With the development of the jaws, the tongue moves inferiorly. Fusion with the nasal septum begins anteriorly during 9th week, extends posteriorly and is completed by 12th week. Bone develops in the anterior part to form the hard palate. The posterior part develops as muscular soft palate. In early fetal period the nose is flat and mandible underdeveloped. They attain their characteristic form during fetal period The enlargement of brain results in the formation of a prominent forehead Eyes initially appear on each side of frontonasal prominence ;move medially Ears first appear on lower portion of lower jaw, grow in upper direction to the level of the eyes.
The three parts of the ear-External -Middle and -Internal ,arise from separate ,diverse embryonic origins. The external ear forms around the first branchial groove which deepens to become the external acuostic meatus.
This is the first sensory organ to begin development. The light sensitive portion of the eye retina ,is the outgrowth from the forebrain ,projecting bilaterally as the optic vesicles which are connected to the brain by the optic stalks, this results in a thickening called as lens placodes.
These placodes invaginates in its centre by the development of peripheral folds. The optic vesicles invaginate partly to form the double layered optic cusps and the optic stalk becomes the optic nerve.
The outer layer of the optic cup acquires pigmentation to become the pigmented layer of the retina. Lower lip :The mandibular processes of the two sides grow towards each other and fuse in the midline ,they form the lower margin of the stomatodeum.
Upper lip :Each maxillary process now grows medially and fuses, first with the lateral nasal process and the with the medial nasal process. The mesodermal basis of the lateral part of the lip is formed from the maxillary process. The overlying skin is derived from the ectoderm covering this process. The muscles of the face including those of the lips are derived from the 2nd branchial arch and are supplied by the facial nerve.
The three swellings orginate from the 1st pharyngeal arch. As the 3 swellings increase in size ,they overgrow the tuberculum impar and merge with each other thus forming the anterior two thirds or the body of the tongue. Hypoglossal nerve Chorda tympani branch of. Development of upper lip- at th wk By the fusion of maxillary process and medial nasal process. Add another edition? Human Anatomy Elaine N. Marieb, Patricia Bra Donate this book to the Internet Archive library.
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