nation
of resection with twisting or tearing of the nerve from its central
connections--_avulsion_. To prevent the regeneration of the nerve after
these operations, the canal of exit through the bone should be
obliterated; this is best accomplished by a silver screw-nail driven
home by an ordinary screw-driver (Charles H. Mayo).

When the neuralgia involves branches of two or of all three trunks, or
when it has recurred after temporary relief following resection of
individual branches, the _removal of the semilunar ganglion_, along with
the main trunks of the maxillary and mandibular divisions, should be
considered.

The operation is a difficult and serious one, but the results are
satisfactory so far as the cure of the neuralgia is concerned. There is
little or no disability from the unilateral paralysis of the muscles of
mastication; but on account of the insensitiveness of the cornea, the
eye must be protected from irritation, especially during the first month
or two after the operation; this may be done by fixing a large
watch-glass around the edge of the orbit with adhesive plaster.

If the ophthalmic branch is not involved, neither it nor the ganglion
should be interfered with; the maxillary and mandibular divisions should
be divided within the skull, and the foramen rotundum and foramen ovale
obliterated.

CHAPTER XVII

THE SKIN AND SUBCUTANEOUS TISSUE

Structure of skin--_Blisters_--_Callosities_--_Corns_--_Chilblains_
--_Boils_--_Carbuncle_--_Abscess_--_Veldt sores_--Tuberculosis of
skin: _Inoculation tubercle_--_Lupus_: _Varieties_--Sporotrichosis
--Elephantiasis--Sebaceous cysts or wens--Moles--Horns--New growths:
_Fibroma_; _Papilloma_; _Adenoma_; _Epithelioma_; _Rodent cancer_;
_Melanotic cancer_; _Sarcoma_--AFFECTIONS OF CICATRICES--_Varieties
of scars_--_Keloid_--_Tumours_--AFFECTIONS OF NAILS.

#Structure of Skin.#--The skin is composed of a superficial cellular
layer--the epidermis, and the corium or true skin. The _epidermis_ is
differentiated from without inwards into the stratum corneum, the
stratum lucidum, the stratum granulosum, and the rete Malpighii or
germinal layer, from which all the others are developed. The _corium_ or
_true skin_ consists of connective tissue, in which ramify the blood
vessels, lymphatics, and nerves. That part of the corium immediately
adjoining the epidermis is known as the papillary portion, and contains
the terminal loops of the