We learn that the equator is a line around the wide waist of the world. Pleasure cruisers often make a great toâdo about crossing this line on the ocean. Any passenger who owns up to the fact that this is his first crossing may be put through ceremonies such as walking the plank and other merry goingsâon.
Ectoderm â Outer or External Layer â differentiates into the nervous system, epidermis, and the outer part of the integument system â forms the central nervous system, the lens of the eye, cranial and sensory, the ganglia and nerves, pigment cells, head connective tissues, the epidermis, hair, and mammary glands.
Central Nervous System (CNS) The CNS includes the brain and the spinal cord. The most important parts of the CNS are protected by bones. The skull protects the brain and the spine protects the spinal cord. The nervous system is made up of the CNS and the peripheral nervous system (PNS). The PNS includes the neurons, or nerves, that form a network that carries information to and from the neck and arms, trunk, legs, skeletal muscles, and internal organs.