Related Clues:

• Rock band led by two sisters
• Book's backbone
• Sign of love at the end of 8 down
• It may be seen with a 37-Across
• What a chiropractor manipulates
• Impulse transmitter — bottle
• Pacemaker's place
• Shape carved on a tree, often
• Skeletal axis
• Brass neck
• "The __!"
• Novocaine target
• Pressure around referee, initially, to give red card
• It may be in a bundle
• Symbol after 'I' on many a bumper sticker