embryonic development. This is where the neural plate folds in on itself, forming the neural crest. Neural crest cells will eventually become portions of the peripheral nervous system. During development, the neural tube will considered the precursore to the spinal cord and the rest of the nervous system, eventually becoming the Central Nervous System. The central nervous system can be divided into three classes of neuromeres: prosomeres, mesomeres, and rhombomeres. The forebrain forms the six prosomers, p1 to p6, which are then divided into two more categories, dorsal and ventral. The telencephalon forms from the dorsal parts of p6 and p5, where p6 becomes the olfactory system and p5 will coincide with the visual system. Mesomeres, m1 and m2, become the midbrain, which contains the superior and inferior colliculi. The 12 rhombomeres, which are numbered from r0 to r11, construct the hindbrain. The myelencephalon is made from rhombomeres r2 to r11, which also form the medulla. These rhombomeres are also associated with the neural crest that supplies the pharyngeal arches, a set of visible tissues that are in line with the developing brain and give rise to the head and neck. Spinal Cord Anatomy Spinal segments are the part of the spinal cord, from which ventral and dorsal roots exit to form a specific pair of spinal nerves. The spinal chord is not segmented itself, it is only made into segments by the spinal nerves as they leave. 31 deferent segments exists in a human spinal cord: 8 cervical segments Cervical nerves exit above C1 segment and below C1-C7. Note that this creates 8 nerves and segments corresponding to only 7 cervical vertebra. 12 thoracic segments Nerves exit below T1-T12. 5 lumbar segments Nerves exit below L1-L5. 5 sacral segments Nerves exit below S1-S5. 1 coccygeal segment Originally, during development there are two segments S1 and S2 which fuse. The nerves in this case exit at the coccyx. In more detail The spinal cord is the main pathway for information connecting the brain and peripheral nervous system. The length of the spinal cord is much shorter than the length of the bony spinal column. The human spinal cord extends from the foramen magnum and continues through to the conus medullaris near the second lumbar vertebra, terminating in a fibrous extension known as the filum terminale. It is about 45 cm (18 in) long in men and around 43 cm (17