a figure from the essay
Homeotic Genes and the Evolution of Anthropods and Chordates
by Sean B. Carroll

Figure 5 (from page 81 of Shaking the Tree: Readings from Nature in the History of Life edited by Henry Gee)

Hox genes and the evolution of vertebrate axial morphology. The expression of various Hox genes along the chick and mouse body axes are depicted. The different regions of the respective vertebral columns, that is, cervical (C), thoracic (T), lumbar (L), sacral (S) and caudal (Co), contain different numbers of vertebrae. The anterior expression boundaries of several members of the Hox D cluster mark morphological transitions such as the lumbar/sacral boundary (Hoxd-9-10) and the sacral/caudal transition (Hoxd-11-12); Hoxc-6 expression marks the cervical/thoracic transition in both species, even though it arises at different somite positions. Note that in the chick all members of the ninth paralogous group mark the posterior of the thoracic region (Hoxa-9, b-9, c-9), except for Hoxd-9 which is regulated differently and marks the posterior lumbar region. Adapted from ref. 53.

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About the book: Shaking the Tree: Readings from Nature in the History of Life edited by Henry Gee, published by the University of Chicago Press.