Radical Neck Dissection
All lymph nodes (bean-shaped glands that filter harmful agents picked up by the lymphatic system) from the collar bone to the jaw and from the front of the neck to the back are removed, along with the sternocleidomastoid muscle (moves the head from side to side), the spinal accessory nerve (involved in speech, swallowing and some head movements), the submandibular gland (one of the salivary glands) and the internal jugular vein. 

Modified or Functional Neck Dissection
All lymph nodes (bean-shaped glands that filter harmful agents picked up by the lymphatic system) from the collar bone to the jaw and from the front of the neck to the back are removed.