101
C H A P T E R
Pharyngeal Apparatus, Face, and Neck
10
102 BEFORE WE ARE BORN ESSENTIALS OF EMBRYOLOGY AND BIRTH DEFECTS
(hyoid) makes a major contribution to the formation of the hyoid bone (see Fig. 10-4B).
Pharyngeal Arch Components
A typical arch has the following components (Fig. 10-3A and B):
•
An arch artery (aortic arch artery) that arises from the truncus arteriosus of the primordial heart and courses around the primordial pharynx to enter the dorsal aorta the primordial pharynx by a bilaminar membrane—theoropharyngeal membrane—composed of fused ectoderm and endoderm. The oropharyngeal membrane ruptures at approximately 26 days (see Fig. 10-1B and C), bringing the primordial pharynx and foregut into communication with the amniotic cavity. The arches contribute exten- sively to the formation of the face, nasal cavities, mouth, larynx, pharynx, and neck (see Fig. 10-2 and Fig. 10-23).
The first arch develops two prominences (see Fig.
10-1B and Fig. 10-2): the smaller maxillary prominence and the larger mandibular prominence. The second arch
Figure 10–1 Illustrations of the pharyngeal apparatus. A, Lateral view showing the develop- ment of four pharyngeal arches. B and C, Ventral (facial) views showing the relationship of the pharyngeal arches to the stomodeum. D, Frontal section through the cranial region of an embryo. E, Horizontal section showing the arch components and the floor of the primordial pharynx. F, Sagittal section of the cranial region of an embryo, showing the openings of the pharyngeal pouches in the lateral wall of the primordial pharynx.
A
D E F
B C
1st pharyngeal pouch
1st pharyngeal pouch Arch 1
Heart Tongue
buds
2 3 1st 4
pharyngeal groove
2nd pharyngeal groove
1st pharyngeal arch
Level of section E
Plane of section F 1 2 34
1 23 28 days
Stomodeum
26 days 28 days
Maxillary prominence
Maxillary prominence
Forebrain
Foramen cecum Ruptured
oropharyngeal membrane Heart prominence
Stomodeum Nasal placode
2nd pharyngeal arch Mandibular
prominence
Mandibular
prominence Arch artery
Ectoderm Endoderm
Germ Layer Derivatives
Mesoderm Pharynx
Notochord
Dorsal aorta Site of closure of
neural groove
1st pharyngeal
membrane Esophagus Laryngotracheal groove
Former site of oropharyngeal membrane
Notochord 1st pharyngeal arch
Arch muscle Arch nerve
Stomodeum
C H A P T E R 10 PHARYNGEAL APPARATuS, FACE, AND NECk 103
Figure 10–2 A Carnegie stage 13, 412-week human embryo.
Stomodeum Maxillary prominence Mandibular prominence Cervical sinus
Heart Second pharyngeal arch Second pharyngeal groove Third pharyngeal arch
Figure 10–3 A, Illustration of the pharyngeal pouches and pharyngeal arch arteries.
B, Horizontal section through the embryo showing the floor of the primordial pharynx and illustrating the germ layer origin of the pharyngeal arch components.
A
B Midbrain
Level of section B
1st pharyngeal pouch Pharyngeal arch arteries (1st to 4th)
Esophagus Respiratory bud
Thyroid diverticulum
(primordium of thyroid gland)Heart
1st arch
2nd arch Cartilages
Muscle Nerve
1st pharyngeal membrane
2nd pharyngeal pouch
3rd pharyngeal pouch 4th pharyngeal arch
3rd pharyngeal arch artery Truncus arteriosus (common arterial trunk from heart)
Dorsal aorta
Ectoderm Endoderm
Germ Layer Derivatives
Mesoderm
C H A P T E R 10 PHARYNGEAL APPARATuS, FACE, AND NECk 103.e1
(Courtesy the late Professor Emeritus Dr. K.V. Hinrichsen, Med- izinische Fakultät, Institut für Anatomie, Ruhr-Universität Bochum, Bochum, Germany.)
104 BEFORE WE ARE BORN ESSENTIALS OF EMBRYOLOGY AND BIRTH DEFECTS
•
A cartilaginous rod that forms the skeleton of the arch•
A muscular component that is the primordium of the muscles in the head and neck•
A nerve that supplies the mucosa and muscles derived from each archDerivatives of Pharyngeal Arch Arteries
The transformation of the arch arteries into the adult arterial pattern of the head and neck is described in the section on the pharyngeal arch artery derivatives in Chapter 14.
Derivatives of Pharyngeal Arch Cartilages The dorsal end of the first arch cartilage becomes ossified to form two middle ear bones, the malleus and incus (Fig.
10-4 and Table 10-1). The middle section of the cartilage regresses, but its perichondrium forms the anterior liga- ment of the malleus and sphenomandibular ligament (see Fig. 10-4B). Ventral parts of the first arch cartilage form the horseshoe-shaped primordium of the mandible. Each half of the mandible forms lateral to and in close associa- tion with its cartilage. The cartilage disappears as the mandible develops around it by intramembranous ossifi- cation (see Chapter 15).
The dorsal end of the second arch cartilage contributes to the stapes of the middle ear and the styloid process of the temporal bone. The part of the cartilage between the styloid process and the hyoid bone regresses; its perichon- drium forms the stylohyoid ligament. The ventral end of the second arch cartilage ossifies to form the lesser cornu of the hyoid bone.
The third arch cartilage ossifies to form the greater cornu of the hyoid bone. (The body of the hyoid forms
Figure 10–4 A, Schematic lateral view of the head, neck, and thoracic regions of a 4-week embryo, showing the location of the cartilages in the pharyngeal arches. B, Similar view of a 24-week fetus, showing the adult derivatives of the arch cartilages. Note that the mandible is formed by intramembranous ossification of mesenchymal tissue surrounding the first arch cartilage.
1st pharyngeal arch
(Meckel) cartilage 2nd pharyngeal arch cartilage
Anterior ligament of malleus
Malleus
Incus Auditory ossicles Stapes
Styloid process Stylohyoid ligament Greater cornu (horn) of hyoid bone Thyroid cartilage Cricoid cartilage Spine of
sphenoid bone
Spheno- mandibular ligament Former site of 1st arch (Meckel)
cartilage Lesser cornu of hyoid bone Body of hyoid bone Site of
developing internal ear
A B
First arch cartilage
Second arch cartilage
Third arch cartilage
Fourth and sixth arch cartilages
from the hypopharyngeal eminence—see Development of Tongue.) The fourth and sixth arch cartilages fuse to form the laryngeal cartilages, except for the epiglottis. The epiglottic and thyroid cartilages appear to develop from neural crest cells (see Fig. 10-21A to C). The cricoid car- tilage develops from mesoderm.
Derivatives of Pharyngeal Arch Muscles
The muscular components of the arches form various muscles in the head and neck; for example, the muscula- ture of the first arch forms the muscles of mastication and others (Fig. 10-5A and B and Table 10-1).
Derivatives of Pharyngeal Arch Nerves
Each arch is supplied by its own cranial nerve (CN). The special visceral efferent (branchial) components of the cranial nerves supply muscles derived from the pharyn- geal arches (Fig. 10-6A and Table 10-1). Because the mesenchyme from the pharyngeal arches contributes to the dermis and mucous membranes of the head and neck, these areas are supplied with the special visceral afferent nerves. The facial skin is supplied by the fifth cranial nerve (CN V, or trigeminal nerve); however, only the caudal two branches (maxillary and mandibular) supply derivatives of the first pharyngeal arch (see Fig. 10-6B).
CN V is the principal sensory nerve of the head and neck and is the motor nerve for the muscles of mastication. Its sensory branches innervate the face, teeth, and mucous membranes of the nasal cavities, palate, mouth, and tongue (see Fig. 10-6C). The seventh cranial nerve (CN VII, or facial nerve), the ninth cranial nerve (CN IX, or glossopharyngeal nerve), and the 10th cranial nerve (CN X, or vagus nerve) supply the second, third, and caudal
C H A P T E R 10 PHARYNGEAL APPARATuS, FACE, AND NECk 105
Figure 10–5 A, Lateral view of the head, neck, and thoracic regions of a 4-week embryo showing the muscles derived from the pharyngeal arches. The arrow shows the pathway taken by myoblasts from the occipital myotomes to form the tongue musculature. B, The head and neck regions of a 20-week fetus, showing the muscles derived from the pharyngeal arches. Parts of the platysma and sternocleidomastoid muscles have been removed to show the deeper muscles. Note that myoblasts from the second arch migrate from the neck to the head, where they give rise to the muscles of facial expression. These muscles are supplied by the facial nerve (cranial nerve VII), the nerve of the second pharyngeal arch.
Occipital myotomes
Orbicularis oculi Temporalis
Occipitalis Auricularis
Stylohyoid Stylopharyngeus Anterior and posterior bellies of digastric muscle
Platysma Orbicularis oris
Masseter Mylohyoid
Pharyngeal muscles
Sternocleidomastoid Clavicle Frontalis
Buccinator
A B
First arch muscles
Second arch muscles
Third arch muscles
Fourth and sixth arch muscles Table 10–1 Structures Derived from Pharyngeal Arch Components*
ARCH NERVE MUSCLES SKELETAL STRUCTURES LIGAMENTS
First (mandibular) Trigeminal† (CN V) Muscles of mastication‡ Mylohyoid and anterior belly
of digastric Tensor tympani Tensor veli palatini
Malleus Incus
Anterior ligament of malleus Sphenomandibular
ligament Second (hyoid) Facial (CN VII) Muscles of facial expression§
Stapedius Stylohyoid
Posterior belly of digastric
Stapes (portion) Styloid process
Lesser cornu of hyoid bone
Stylohyoid ligament
Third Glossopharyngeal (CN IX) Stylopharyngeus Greater cornu of hyoid bone Fourth and sixth‖ Superior laryngeal branch
of vagus (CN X) Recurrent laryngeal
branch of vagus (CN X)
Cricothyroid Levator veli palatini Constrictors of pharynx Intrinsic muscles of larynx Striated muscles of esophagus
Thyroid cartilage Cricoid cartilage Arytenoid cartilage Corniculate cartilage Cuneiform cartilage
*The derivatives of the pharyngeal arch arteries are described in Chapter 14.
†The ophthalmic division of the fifth cranial nerve (CN V) does not supply any pharyngeal arch components.
‡Temporalis, masseter, medial, and lateral pterygoids.
§Buccinator, auricularis, frontalis, platysma, and orbicularis oris and oculi.
‖The fifth pharyngeal arch regresses. The cartilaginous components of the fourth and sixth arches fuse to form the cartilages of the larynx.
106 BEFORE WE ARE BORN ESSENTIALS OF EMBRYOLOGY AND BIRTH DEFECTS
(fourth to sixth) arches, respectively. The superior laryn- geal branch of the vagus nerve supplies the fourth arch, whereas its recurrent laryngeal branch supplies the sixth arch. The nerves of the second to sixth pharyngeal arches (see Fig. 10-6A) innervate the mucous membranes of the tongue, pharynx, and larynx (see Fig. 10-6C).