Skeletal and Muscular Systems Embryology Questions

Accessory ribs are most commonly attached to lumbar vertebrae. When present (incidence
0.5%–1%), a cervical rib is usually attached to the seventh cervical vertebra. Cervical ribs
may compress the brachial plexus and subclavian vessels and cause superior thoracic outlet
syndrome

Osteogenesis imperfecta is a deficiency of type I collagen and results in spontaneous
fractures of fetal bones and blue sclera of the eye

The tongue muscles (intrinsic and extrinsic) arise from the occipital somites (myotomes).

Because the biceps femoris muscle is a flexor of the leg, it develops from the anterior
condensation of myotomic mesoderm.

The extrinsic eye muscles arise from the preotic somites (myotomes) found near the
prochordal plate. Recent research indicates that the extrinsic eye muscles are derived from
somitomeres 1–3, and 5.

When the pedicles fail to fuse with the vertebral body, a condition called spondylolisthesis
results. This allows the vertebral body to move anterior with respect to the vertebrae below it,
causing lordosis.

The anterior fontanelle is usually closed by 2 years of age; the posterior and sphenoid
fontanelles are usually closed by the end of 6 months of age.

Brachycephaly is the premature closure of the coronal sutures, which leads to a
square-shaped skull with a short occipital–frontal diameter.

Because the biceps brachii muscle is a flexor of the antebrachium (forearm), it develops from
the anterior condensation of myotomic mesoderm.