Intermaxillary Segment

Philtrum Embryo
Philtrum
Intermaxillary Segment Embryology
Figure 15.23 Frontal aspect of the face. A. 7-week embryo. Maxillary prominences have fused with the medial nasal prominences. B. 10-week embryo. C. Scanning electron micrograph of a human embryo at a stage similar to that of A.

table 15.2 Structures Contributing to Formation of the Face

Prominence

Structures Formed

Frontonasala Forehead, bridge of nose, medial and lateral nasal prominences

Maxillary Cheeks, lateral portion of upper lip

Medial nasal Philtrum of upper lip, crest and tip of nose

Lateral nasal Alaeofnose

Mandibular Lower lip a The frontonasal prominence is a single unpaired structure; the other prominences are paired.

Fusion Maxillary Prominence
Figure 15.24 A. Intermaxillary segment and maxillary processes. B. The intermaxillary segment giving rise to the philtrum of the upper lip, the median part of the maxillary bone with its four incisor teeth, and the triangular primary palate.

outgrowths from the maxillary prominences. These outgrowths, the palatine shelves, appear in the sixth week of development and are directed obliquely downward on each side of the tongue (Fig. 15.25). In the seventh week, however, the palatine shelves ascend to attain a horizontal position above the tongue and fuse, forming the secondary palate (Figs. 15.26 and 15.27).

Anteriorly, the shelves fuse with the triangular primary palate, and the incisive foramen is the midline landmark between the primary and secondary palates (Fig. 15.27B). At the same time as the palatine shelves fuse, the nasal septum grows down and joins with the cephalic aspect of the newly formed palate (Fig. 15.27).

CLINICAL CORRELATES Facial Clefts

Cleft lip and cleft palate are common defects that result in abnormal facial appearance and defective speech. The incisive foramen is considered the dividing landmark between the anterior and posterior cleft deformities. Those anterior to the incisive foramen include lateral cleft lip, cleft upper jaw, and cleft between the primary and secondary palates (Figs. 15.28, B and D, and 15.29, A and B). Such defects are due to a partial or complete lack of fusion of the maxillary prominence with the medial nasal prominence on one or both sides. Those that lie posterior to the incisive foramen include cleft (secondary) palate and cleft uvula (Figs. 15.28E and 15.29, C and D). Cleft palate results from a lack of fusion of the palatine shelves, which may be due to smallness of the shelves, failure of the shelves to elevate, inhibition of the fusion process itself, or failure of the tongue to drop from between the shelves because of micrognathia. The third category is formed by a combination of clefts lying anterior as well as posterior to the incisive foramen (Fig. 15.28F).

Incisive Foramen Position

Figure 15.25 A. Frontal section through the head of a 6.5-week-old embryo. The palatine shelves are in the vertical position on each side of the tongue. B. Ventral view of the palatine shelves after removal of the lower jaw and the tongue. Note the clefts between the primary triangular palate and the palatine shelves, which are still vertical.

C. Scanning electron micrograph of a mouse embryo at a stage similar to that of A.

D. Palatal shelves at a stage slightly older than those in B. The shelves have elevated, but they are widely separated. The primary palate has fused with the secondary palatal shelves.

Figure 15.25 A. Frontal section through the head of a 6.5-week-old embryo. The palatine shelves are in the vertical position on each side of the tongue. B. Ventral view of the palatine shelves after removal of the lower jaw and the tongue. Note the clefts between the primary triangular palate and the palatine shelves, which are still vertical.

C. Scanning electron micrograph of a mouse embryo at a stage similar to that of A.

D. Palatal shelves at a stage slightly older than those in B. The shelves have elevated, but they are widely separated. The primary palate has fused with the secondary palatal shelves.

Anterior clefts vary in severity from a barely visible defect in the vermilion of the lip to extension into the nose (Fig. 15.29A). In severe cases the cleft extends to a deeper level, forming a cleft of the upper jaw, and the maxilla is split between the lateral incisor and the canine tooth. Frequently such a cleft extends to the incisive foramen (Fig. 15.28, C and D). Likewise, posterior clefts vary in severity from cleavage of the entire secondary palate (Fig. 15.29D) to cleavage of the uvula only.

Oblique facial clefts are produced by failure of the maxillary prominence to merge with its corresponding lateral nasal prominence. When this occurs, the nasolacrimal duct is usually exposed to the surface (Fig. 15.29£).

Median cleft lip, a rare abnormality, is caused by incomplete merging of the two medial nasal prominences in the midline. This anomaly is usually accompanied by a deep groove between the right and left sides of the nose

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Horizontal Facial Cleft

Figure 15.26 A. Frontal section through the head of a 7.5-week embryo. The tongue has moved downward, and the palatine shelves have reached a horizontal position. B. Ventral view of the palatine shelves after removal of the lower jaw and tongue. The shelves are horizontal. Note the nasal septum. C. Scanning electron micrograph of a mouse embryo at a stage similar to that of A. D. Palatal shelves at a stage similar to that of B.

Figure 15.26 A. Frontal section through the head of a 7.5-week embryo. The tongue has moved downward, and the palatine shelves have reached a horizontal position. B. Ventral view of the palatine shelves after removal of the lower jaw and tongue. The shelves are horizontal. Note the nasal septum. C. Scanning electron micrograph of a mouse embryo at a stage similar to that of A. D. Palatal shelves at a stage similar to that of B.

(Fig. 15.29F). Infants with midline clefts are often mentally retarded and may have brain abnormalities that include varying degrees of loss of mid-line structures. Loss of midline tissue may be so extensive that the lateral ventricles fuse (holoprosencephaly). These defects are induced very early in development, at the beginning of neurulation (days 19-21) when the midline of the forebrain is being established.

Most cases of cleft lip and cleft palate are multifactorial. Cleft lip (approximately 1/1000 births) occurs more frequently in males (80%) than in females; its incidence increases slightly with maternal age, and it varies among populations. If normal parents have one child with a cleft lip, the chance that the next baby will have the same defect is 4%. If two siblings are affected, the risk for the next child increases to 9%. If one of the parents has a cleft lip and they have one child with the same defect, the probability that the next baby will be affected rises to 17%.

Primary And Secondary Palate

Primary palate

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Primary palate

Primary PalatePrimary And Secondary PalatePalatal Shelves Fusion

Figure 15.27 A. Frontal section through the head of a 10-week embryo. The two palatine shelves have fused with each other and with the nasal septum. B. Ventral view of the palate. The incisive foramen forms the midline between the primary and secondary palate. C. Scanning electron micrograph of the palatal shelves of a mouse embryo at a stage similar to that of B.

Figure 15.27 A. Frontal section through the head of a 10-week embryo. The two palatine shelves have fused with each other and with the nasal septum. B. Ventral view of the palate. The incisive foramen forms the midline between the primary and secondary palate. C. Scanning electron micrograph of the palatal shelves of a mouse embryo at a stage similar to that of B.

The frequency of isolated cleft palate is much lower than that of cleft lip (1/2500 births), occurs more often in females (67%) than in males, and is not related to maternal age. If the parents are normal and have one child with a cleft palate, the probability of the next child being affected is about 2%. If, however, there is a similarly affected child and a relative or parent both with a cleft palate, the probability increases to 7% and 15%, respectively. In females, the palatal shelves fuse approximately 1 week later than in males. This difference may explain why isolated cleft palate occurs more frequently in females than in males. Anticonvulsant drugs, such as phenobarbital and diphenylhydantoin, given during pregnancy increase the risk of cleft palate.

Primary Palate Incisive Foramen Uvula

Figure 15.28 Ventral view of the palate, gum, lip, and nose. A. Normal. B. Unilateral cleft lip extending into the nose. C. Unilateral cleft involving the lip and jaw and extending to the incisive foramen. D. Bilateral cleft involving the lip and jaw. E. Isolated cleft palate. F. Cleft palate combined with unilateral anterior cleft lip.

Figure 15.28 Ventral view of the palate, gum, lip, and nose. A. Normal. B. Unilateral cleft lip extending into the nose. C. Unilateral cleft involving the lip and jaw and extending to the incisive foramen. D. Bilateral cleft involving the lip and jaw. E. Isolated cleft palate. F. Cleft palate combined with unilateral anterior cleft lip.

Cleft Lip Scan
Figure 15.29 A. Incomplete cleft lip. B. Bilateral cleft lip. C. Cleft lip, cleft jaw, and cleft palate. D. Isolated cleft palate. E. Oblique facial cleft. F. Midline cleft lip.

Wall of brain

Nasal pit

Medial nasal prominence

Bacterial Vaginosis Facts

Bacterial Vaginosis Facts

This fact sheet is designed to provide you with information on Bacterial Vaginosis. Bacterial vaginosis is an abnormal vaginal condition that is characterized by vaginal discharge and results from an overgrowth of atypical bacteria in the vagina.

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Responses

  • ernest
    Where is the vertical foramen located?
    7 years ago

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