Final answer:
The nerve formed by the union of the ventral rami of C5 and C6 is the musculocutaneous nerve (option d) , which innervates the anterior compartment of the forearm and the skin of the lateral forearm.
Step-by-step explanation:
The student is asking about the nerve that is formed by the union of the ventral rami of the fifth and sixth cervical spinal nerves (C5 and C6). This question is specific to the subject of anatomy, which falls within the realm of medicine. The brachial plexus is a network of nerves that supplies the upper limb. The ventral rami of spinal nerves C5 and C6 contribute to the formation of several nerves, including the axillary nerve and the radial nerve, among others.
However, the nerve specifically formed by the union of the C5 and C6 ventral rami is not the axillary nerve, radial nerve, or median nerve - these nerves receive contributions from other spinal nerve roots as well. Instead, the correct answer is the musculocutaneous nerve, which is primarily responsible for innervating muscles in the anterior compartment of the forearm and the skin of the lateral forearm.
In summary, the musculocutaneous nerve is the one that emerges from the combination of the C5 and C6 ventral rami.