Haversian canals (also called central canals) run longitudinally through the bone and contain blood vessels and nerves which supply the bone.
Business casual: Generally means khaki pants, a plain polo shirt or a long-sleeved casual button-down oxford shirt, a V-neck sweater, sometimes a sports coat or blazer, and brown leather shoes. Loafers are a good choice, and you should wear socks.
Khakis or casual slacks with a polo shirt are the rule of thumb when it comes to elegant casual day wear for men. If the resort or cruise is more upscale, your leisure wear need not be more formal, but perhaps of better design and quality. Ball caps and sneakers are fine, as long as they stay outdoors.