Some primitive streak derived mesoderm forms the caudal eminence. It is situated caudal to the neurenteric canal in the tail bud region. This structure is apparently not described by any authors at this stage except Müller F., O'Rahilly R., (1983). It is the site of secondary neuralation which is illustrated in Larsen W.J.,(1993) pp.73-74 and figs 4.11 and 3.10
The caudal eminence has developed an axial condensation, where the caudal notochord will later form, and paraxial condensations which form the caudalmost somites. During this stage it contributes 10-5% of the total length of the embryo.
Between the caudal border of the caudal neuropore or its site, and the cloacal membrane, the eminence contains two main types of tissue.
1 Dense, radially arranged cells which are the precursor of the neural tube. Vacuoles develop within these cell clusters and coalesce to form the neural canal which extends into the caudal eminence. Dense areas also indicate where the hindgut and notochord will form.
2. Laterally, looser mesenchyme has not yet formed somites. Müller F., O'Rahilly R., (1987)
The caudal eminence lies caudal to the cloacal membrane, it contains a somitic plate which, in embryos of more than 34 somites meets in the median plane. 0-5 pairs of somites may have differentiated within this region. Hindgut, notochord and neural tube continue to develop in the area. Müller F., O'Rahilly R., (1988b)
No further references are found to this structure. It is therefore presumed that the mesenchyme in this area has entirely differentiated into somites, hindgut, notochord and neural tube.