A system of surgery . but certain small tumours areoccasionally observed in the hands and fingers, which havebeen described as dermal cysts, sebaceous cysts, or digital der-moids. In structurethese tumourspresent a centralcavity containingepithelial debrisand a lining ofskin; indeed,when examinedmicroscopically,they appear asif a piece of skinhad been invertedinto the subcu-taneous tissue (Shattock). Thesetumours areknown as im-plantation cysts,as there is everyreason to believethat they areproduced by smallpieces of skin ac-cidentally trans-planted by in-jury, especiallypricks by sharpinstrum
A system of surgery . but certain small tumours areoccasionally observed in the hands and fingers, which havebeen described as dermal cysts, sebaceous cysts, or digital der-moids. In structurethese tumourspresent a centralcavity containingepithelial debrisand a lining ofskin; indeed,when examinedmicroscopically,they appear asif a piece of skinhad been invertedinto the subcu-taneous tissue (Shattock). Thesetumours areknown as im-plantation cysts,as there is everyreason to believethat they areproduced by smallpieces of skin ac-cidentally trans-planted by in-jury, especiallypricks by sharpinstruments, suchas awls, needles,forks, etc. Theyalso occur in cicatrices. Implantation cysts are usually of the size of cherry-stones, but they may reach the size of bantams eggs. These tumours are not confined to the limbs ; they have beenobserved on the trunk, scalp, and face. Yery many exampleshave been reported in the cornea and iris, the results of punc-tured wounds, injuries and operations on the eyeball. DetachedQ*. Fig. 130.—Dermoid situated over the Junction of the Manubriumand Gladiolus ; there is a dermoid over the left cornu of thehyoid bone. (After Bramann.) 490 Tumours. conjunctival epithelium and eyelashes carried in and transplantedon the vascular iris may grow into tumours. 2. Tubulo-dermoids.—There exist in the human embryo certaincanals and passages, many of which normally disappear befoi*e of these obsolete canals—the thyro-glossal duct, the branchialclefts, and the post-anal gut—are occasionally the source of dermoids. Lingual dermoids, especially those situated between the genio-hyo-glossi muscles and attached to the hyoid bone, doubtless arise inpersistent portions of the buccal extremity of the thyro-glossal situated deeply in the substance of the tongue have beenfrequently mistaken for sebaceous cysts. They sometimes attainvery large proportions, and bulge from the mouth. Occasionally,dermoids arising in the lingual segment
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