41 6 Tumors. 



fmm simple retention of their contents and dilatation of their 

 canals and are not formed in the loose structures of the body from 

 exudation into them or from liquefaction of the tissues themselves, 

 but take their inception in early embryonic life from displaced and 

 isolated portions of organs, organic rests and hollow ofifshoots of 

 such structures, and acquire an independence of growth. 



The simplest type of these cysts is the epidermoid cystoma or 

 epithelioma cysticum, a sac of the size of a nut, a hen's egg or even 

 of a fist, which is completely filled with loosened squamous epider- 

 mal cells almost all in a keratous condition; sometimes cholesterin 

 is found mixed in with these. Bonnet met a genuine example of this 

 type in the cranial cavity of a horse. All these cysts containing 

 squamous epithelium doubtless originate from ectodermal cellular 

 inclusions in foetal life, conceivable as occurring from friction of the 

 skin by amniotic strands. Their occurrence in the cranial vault, near 

 the aural and temporal region, suggests that displaced portions of 

 the epithelium of the branchial arches constituted their original sub- 

 stance, and in case of those developing in the brain, from the med- 

 ullar}- folds, the ectoderm must certainly play a part in their 

 origin. Experimental studies by Schweninger, E. Kaufmann and 

 Ribbert show that epithelial cysts can be readily produced artifi- 

 cially by insertion of a bit of epiderm, conjunctiva or tracheal mu- 

 cous membrane into the peritoneum or under the skin. When the 

 epithelial cells are supported by a little connective tissue to preserve 

 their nutrition they grow over the interior surfaces of the wound 

 with which they have been placed in contact, and form the lining of 

 the hollow space, the latter being occupied by the wound secretions 

 and desquamated epithelium. Epithelial lined cysts may also be 

 produced, as pointed out by these authors, by suturing over a cir- 

 cumscribed bit of epiderm the adjacent loosened borders of skin; 

 the bit of epiderm beneath the sutured parts grows and fills in the 

 space beneath the elevated cutis (Ribbert). In man as the result of 

 accidental misplacement of epithelium in operations, or of cutaneous 

 lacerations, similar cyst formations are well known to occur. Such 

 results are known as traumatic epithelial cysts. 



As derivatives of the skin in its entirety, of the cutis with its 

 glands, of hairs and epiderm, may be mentioned the dermoid cysts 

 or hair follicle tumors (dermatocystis congenita or cystoma der- 

 moides), which occur comparatively frequently in cattle and horses, 

 situated in the subcutaneous connective tissue. They appear from 

 the exterior as flat cutaneous swellings or may be found acci- 

 dentally in skinning or eating beef. The cyst varies from the size 



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