Well I’m no physician but I would think an epidermal cyst would be located in/on/about the epidermis, and how did that get fossilized and survive all those thousands of years in the North Sea?
I believe they said it was rare in modern populations. Reading this, I’m glad of that:
Epidermal cyst and osteolysis of the cranial vault [Article in French]
Guillaud V, Remond J, Balme B, Moulin G.
Service de Dermatologie, Hopital de l’Antiquaille, Lyon.
http://www.ncbi.nlm.nih.gov/pubmed/1304688
In a 40-year old man undergoing, under local anaesthesia, excision of an epidermal cyst located in the frontal region, at the border of the scalp, the operator had difficulties in removing the deep part of the cyst and perceived an underlying bone depression. The depression was caused by a 2 x 1.3 cm wide lacuna in the calvarium, which was subsequently treated by neurosurgeons. Histology showed only fragments of a simple epidermal cyst wall and no evidence of dermoid cyst. The causes of osteolysis associated with congenital or acquired skin lesions are reviewed. In this case, the old age and volume of the cyst may explain the osteolysis by mechanical compression. This case is exceptional since we were unable to find other examples in the literature, apart from dermoid and trichilemmal cysts.