Fig. 3.

Metazoan conceptual longitudinal axis is quite variable in embryos and adults. (A) Adult human in comparative anatomical position for easy comparison with other vertebrates (Fig. 2B) and application of the same positional descriptors. Also note the difference between topographic and systems body descriptions (Fig. 1). The former includes head (h), neck (n), trunk (t), upper limb (ul), and lower limb (ll) divisions; an example of the latter is the CNS (color-coded as in B and Fig. 2B) extending across body divisions. [Reprinted from Basic Neurology, J.P. Schade & D.H. Ford, page 15, Copyright (1965).] (B) Neural tube of a 4-wk-old human embryo (dashed line is longitudinal–rostrocaudal axis). The top is the right half of the neural tube with topographic divisions (Fig. 1 Left) color-coded to match a conceptualized straightened neural tube (bottom half) in frontal section (Fig. 2B). C, caudal; D, dorsal; EB, endbrain; FB, forebrain; HB, hindbrain; IB, interbrain; MB, midbrain; MY, medulla (afterbrain); R, rostral; RB, rhombicbrain; SP, spinal cord; V, ventral. A is adapted with permission from ref. 40; the photo in B is adapted from ref. 41.