Possible Clues:

• Bone below a humerus
• Thinner of two long bones in forearm
• The longer of two bones in the forearm
• Car document; ticket book
• It's near the 17-Across
• The longer and inner bone in forearm
• It runs down your arm
• One out on a limb
• Learner driver breaking girl's bone
• Wonderful Natalie - not all bone!