Chapter 19 - Upper Limb

Question 1

Which of the following arteries is one of
the first branches to form from the axis
artery?

(A) Radial artery
(B) Ulnar artery
(C) Axillary artery
(D) Median artery
(E) Brachial artery

Answer 1

D. Median Artery

The median artery is one of the first branches to form from the axis artery. In the adult,
the median artery does not persist and is probably reduced to a small unnamed vessel. This
is why the median nerve does not have an accompanying artery in the adult like the ulnar
nerve (ulnar artery) and radial nerve (radial artery).

Question 2

The humerus develops from which of the
following?

(A) Somite mesoderm
(B) Lateral plate mesoderm
(C) Intermediate mesoderm
(D) Extraembryonic mesoderm
(E) Sclerotome mesoderm

Answer 2

B. Lateral Plate Mesoderm

All bones of the upper limb form from lateral plate mesoderm that condenses alone the
central axis of the upper limb bud.

Question 3

The long head of the triceps muscle
develops from which of the following?

(A) Posterior condensation
(B) Anterior condensation
(C) Lateral plate mesoderm
(D) Extraembryonic mesoderm
(E) Sclerotome mesoderm

Answer 3

A. Posterior condensation

Somite mesoderm migrates into the limb bud and forms two condensations. The posterior
condensation of the upper limb gives rise to the extensors of the upper limb, which
attain a posterior location in the adult because of the lateral rotation of 90.

Question 4

Which of the following muscles will the
lateral cord of the brachial plexus innervate?

(A) Triceps
(B) Supinator
(C) Extensor carpi ulnaris
(D) Extensor digitorum
(E) Biceps brachii

Answer 4

E. Biceps brachii

One of the nerves that form from the lateral cord of the brachial plexus is the musculocutaneous
nerve. The musculocutaneous nerve will innervate muscles derived from the
anterior condensation (flexors). The biceps brachii muscle is a flexor at the elbow joint.
Note that the biceps brachii muscle and the musculocutaneous nerve are related
embryologically to the anterior condensation and anterior divisions (which form the lateral
cord) and in the adult are located anterior. This occurs because of the lateral rotation of 90.

Question 5

During weeks 6–8, the upper limb will
rotate

(A) Medially 90
(B) Laterally 90
(C) Medially 180
(D) Laterally 180
(E) No rotation occurs

Answer 5

B. Laterally 90

The upper limb rotates laterally 90 so that the elbows point posteriorly.