Across
- 4. Control center of the nervous system
- 5. Long bone in the upper arm
- 6. Smallest unit of a nerve cell
- 7. Main muscle for breathing
- 9. Circular muscle that controls the passage of food
- 13. Pumping organ of the circulatory system
- 14. Protective outer layer of the eye
- 16. Chamber that pumps blood to the lungs
- 17. Body's largest organ
- 18. Primary female reproductive organ
Down
- 1. Fluid-filled sac that reduces friction between bones
- 2. Connects muscles to bones
- 3. Chemical messengers in the body
- 4. Spongy tissue inside bones
- 8. Tube connecting the mouth and stomach
- 10. Gland that produces insulin
- 11. Butterfly-shaped gland in the neck
- 12. Main organ of the respiratory system
- 15. Bean-shaped organ that filters blood