DEBMOIDS. 75 



ulceration and fungation. Further, they disseminate rapidly 

 to the lymphatic glands near by, by the lymph stream, and to 

 distant organs by the vascular system. 



DERMOIDS AND TERATOMATA. 



In the vast majority of dermoids, skin or dermal tissue forms 

 the basis of the tumour. They may be classified in four 

 varieties : sequestration dermoids, tubulo-dermoids, ovarian or 

 testicular dermoids, and dermoid patches. A knowledge of 

 developmental anatomy explains many of the points observable 

 concerning dermoids. 



Sequestration Dermoids. If the surface epithelium becomes 

 included in the deeper tissues a dermoid is likely to be formed. 

 Hence it will be readily seen that such dermoids occur where 

 there is the greatest chance for portions of epithelium to become 

 sequestrated. The middle line of the body is therefore a common 

 situation, seeing that there is here a junction of the two halves 

 of the foetus. In the process of fusion, small portions of epithelium 

 may be cut off by mesoblastic tissue from the surface and thus 

 become buried, and therefore middle line sequestration dermoids 

 are easily explained. On the dorsal aspect they are most often seen 

 in the region of the sacrum and coccyx, where also dimples and 

 pits may be observed and may be considered as abortive attempts 

 to sequestrate surface epithelium. Dermoid cysts in this region 

 which have suppurated and discharged explain at least one form 

 of persistent sacral sinus. In the median line on the ventral 

 aspect dermoids are more common. Occasionally they are found 

 within the thorax, epithelium having been caught by the closing 

 sternum, and thus deeply buried. In addition, those facial and 

 branchial fissures which are found in the face and neck 

 frequently and easily become the sites of inclusion of epiblast. 

 The commonest situation for a facial dermoid is just above the 

 outer canthus of the eye, that is at the external extremity of the 

 orbito-nasal fissure. Sometimes this cyst may have a deep pro- 

 cess passing through the bone and into the cranium, hence the 



