Test 42    (Embryology)

1. The following structures are derived from the first pharyngeal arch:

a. muscle of facial expression

b. stapes

c. malleus 

d. incus

e. external auditory meatus

Answera.F   b.F   c.T  d.T   e.F
The muscles of facial expression, stapes, stylohyoid ligament and stylohyoid muscles are derived from the second pharyngeal arch. The external auditory meatus
is derived from the first pharyngeal cleft.

 

2. Bones in the skull that develop in membrane include:

a. frontal bone

b. body of sphenoid

c. parietal bone

d. mastoid of temporal bone

e. mandible

Answera.T   b.F   c.T   d.F   e.F
The vault of the cranium forms in membrane and includes frontal, parietal and occipital bone.
Sphenoid, mastoid of temporal bone and mandible develop in cartilage.
 

3. Structures that originate from neural crest cells include:

a. ciliary muscle

b. corneal stroma

c. corneal endothelium

d. choroidal melanocytes

e. optic nerve

Answera.F   b.T   c.T   d.T   e.F
Ciliary muscle is derived from mesoderm and the optic nerve from the neuroectoderm.

4. With regard to the development of lens:

a. the lens is derived from the ectoderm

b. the lens placode first formed at 22 days gestation

c. the lens fibres in the embryo is produced entirely from the 
    anterior vesicle cells 

d. the lens sutures are arranged in a Y shape anteriorly and an 
    inverted Y shape posteriorly

e. Mittendorf's dot is remnant of the pupillary membrane

Answera.T   b.T   c.F   d.T   e.F
Initially, the lens fibres in the embryo is produced from the posterior vesicle cells.
Mittendorf's dot is hyaloid remnant on the posterior lens capsule.

5. The following are true:

a. the lacrimal sac develops from the surface ectoderm

b. the lacrimal gland is derived from the mesoderm

c. the eyelids open at 5 months gestation

d. the puncta open into the eyelid after the eyelids have open

e. the orbicularis oculi is formed from the second pharyngeal 
    arch

Answera.T   b.F   c.F   d.F   e.T
The lacrimal gland is derived from the ectoderm.
The eyelids open at 7 months gestation.
The puncta open into the eyelid just before the eyelids become separated.