Development of pharyngeal Arches, Pouches

DEVELOPMENT OF PHARYNGEAL ARCHES AND POUCHES

Q.  Identify the structures marked 1-6 in the following diagram.

Q.  Identify the structures marked 1-18 in the following diagram.

Q.  Identify the structures marked 1- 11 in the following diagram.

Q.  Identify the structures marked 1- 11 in the following diagram.

Q. What are the muscular derivatives of 1st pharyngeal arch?

A.   8 muscles are  derived from 1st pharyngeal arch.

•  4 Muscles of mastication
  • Temporalis
  • Masseter
  • Medial pterygoid
  • Lateral pterygoid
• Tensor tympani
• Tensor palitini
• Mylohyoid
• Anterior belly of diagastric

Q. Which is the nerve of 1st pharyngeal arch?

A. Mandibular  nerve supplies all the muscles derived from 1st pharyngeal arch.

Q.  What is the name of the cartilage of 1st pharyngeal arch? List the skeletal derivatives of 1st pharyngeal arch?

A.  Ist pharyngeal arch cartilage is called Meckel’s cartilage. Following are the skeletal derivatives of 1st pharyngeal arch.

1. Malleus
2. Incus
3. Mandible
4. Maxilla
5. Zygomatic bone
6. Palatine bone
7. Anterior ligament of malleus
8. Sphenomandibular ligament

Q. What  are the muscular derivatives of 2nd pharyngeal arch?

A. Following are the muscular derivatives of 2nd pharyngeal arch?

1. Muscles of facial expression
   • Occipitofrontalis
   • Orbicularis oculi
   • Procerus
   • Corrugator supercilli
   • Nasalis
   • Zygomaticus major
   • Zygomaticus minor
   • Levator labii superioris alequae nasi
   • Levator labi superioris
   • Levator anguli oris
   • Depressor labii inferioris
   • Depressor anguli oris
   • Risorius
   •  Mentalis
2.  Buccinator
3. Platysma
4. Auricular muscles
5.  Stapedius
6.  Stylohoid
7. Posterior belly of diagastric

Q. Why is anterior belly of digastric muscle supplied by mandibular nerve , whereas posterior belly is supplied by facial nerve?

A. This is because anterior belly of digastric muscle is derived from 1st pharyngeal arch and hence  supplied by mandibular nerve , whereas posterior belly is derived from 2nd pharyngeal arch and is supplied by  the nerve of 2nd pharyngeal arch  i.e.facial nerve?

Q.  Which is the nerve of 2nd pharyngeal arch?

A. Facial nerve

Q. Name the cartilage of 2nd pharyngeal arch. List the skeletal derivatives of 2nd pharyngeal arch.

A. Reichert’s cartilage. Following are the skeletal derivatives of 2nd pharyngeal arch.

1. Stapes
2. Styloid process
3. Stylohyoid ligament
4. Lesser cornu of hyoid
5. Upper half of body of hyoid

Q. What are the muscular derivatives of 3rd pharyngeal arch?

A. Only one muscle is derived from the 3rd pharyngeal arch i.e. stylopharyngeus.

Q. Which is the the nerve of third pharyngeal arch?

A. Glossopharyngeal nerve.

Q. List the skeletal derivatives of 3rd pharyngeal arch.

A. Following are the skeletal derivatives of 3rd pharyngeal arch.

1. Greater cornu of hyoid bone.
2. Lower half of body of hyoid bone.

Q. Name the muscular derivatives of 4th pharyngeal arch.

A. Following are the muscular derivatives of 4th pharyngeal arch.

1. Cricothyroid
2. Muscles of pharynx
3. Muscles of palate except tensor veli palitini.

Q. Which is the nerve of 4th pharyngeal arch?

A. Superior laryngeal branch of vagus nerve.

Q. Name the muscular derivatives of 6th pharyngeal arch.

A. All intrinsic muscles of larynx except cricothyroid

Q. Which is the nerve of 4th pharyngeal arch?

A. Recurrent laryngeal branch of vagus nerve.

Q. What is the fate of 1st pharyngeal pouch?

A. Its ventral part forms the tubotympanic recess. The distal expanded part of the recess forms the tympanic cavity and the narrow proximal/medial part forms auditory/pharyngotympanic) tube.

Q. How do palatine tonsils develop?

A. Palatine tonsils develop from the endoderm of 2nd pharyngeal pouch.  In the 20th week, the surrounding mesenchyme differentiates into lymphoid tissue.

Q. What are the structures derived from 3rd pharyngeal pouch?

A. It gives rise to thymus from the ventral part and inferior parathyroid gland from the dorsal part.

Q. What are the derivatives of fourth pharyngeal pouch?

A.  Superior parathyroid glands.

Q. Why does the inferior parathyroid glands develop from 3rd pharyngeal pouch and superior parathyroids from 4th pharyngeal pouch?

A. Inferior parathyroid glands migrate  downwards along with thymus ( both being derived from  3rd pharyngeal pouch) to a lower position than superior parathyroid glands.

Q. What is derived from 5th pharyngeal pouch?

A. Ultimobranchial body. which gives rise to may be ‘C’ cells of thyroid gland.

Q. What is the cause of branchial/ lateral cervical sinus?

A. Failure of 2nd branchial cleft /groove to obliterate leads to formation of cervical sinus or cyst and  it is usually present at the anterior border of sternocleidomastoid muscle.

Q. What is branchial fistula?

A. Branchial fistula  is an epithelial lined tract, open  at both the ends which occurs due to persistance of cervical sinus. when present , it connects the cervical opening to tonsillar fossa.