Chapter IX

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_Bursæ_ are normal in many well-known situations in the body, but may undergo cystic dilatation and become annoying tumors. In many other places, under the influence of friction or mechanical irritation, there develop bursæ which are known as adventitious. These are sometimes subtendinous, and may communicate alike with joint sheaths and tendon sheaths. These are true cysts of new formation not developed from a pre-existing cavity.

They are largely the effect of peculiar occupation, as in housemaids and carpet-layers there are formed frequently _prepatellar bursæ_, while miners get them upon the elbow, porters upon the shoulder, plasterers upon the forearm, etc. In the same way, by the pressure of ill-fitting boots, an adventitious bursa is developed over the expanded head of the first metacarpal bone, thus forming a condition known as _bunion_.

=Neural Cysts.=--This term has been applied by Sutton to pseudocystic dilatation of certain cavities found in the brain and central nervous system. _Hydrocephalus_ is in one sense a pseudocyst of this variety. Corresponding to it in fetal life is _hydramnios_. Hydrocele or cystic dilatation of the fourth ventricle is well known. _Cranial meningoceles_, which are hernial protrusions of brain membranes, are also pseudocysts, to be included in this category. They will be considered in Chapter XXXVI . _Cephalhematoma_ may be also included in the same way. _Spina bifida_, a condition which will be described in

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