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dicularly to the surface, the teeth of the crown will make a circular track. When this groove is of sufficient depth to keep the instrument from slipping, the central pin is retired and made fast before advancing farther. Now begin again to saw, removing the trephine often to clean its teeth with a brush, and to ascertain the depth of the groove by means of a probe or a quill toothpick.
The color of the dust will change from white to a reddish color when the cancellous tissue is reached.
When the instrument is well advanced in the bone, screw into the small, central hole, made by the pin in the first part of the operation, one of Heine's tirefonds (a small screw with an eye in its head). The screw must not be longer than the circular groove is deep.
Continue to advance with the trephine until the toothpick discloses the complete section of the bone in a part of the groove. The trephine must be slightly slanted and made to saw only on the undivided part.
A Galt's trephine is in the shape of a truncated cone, and becomes wedged as soon as the bone is completely severed, hence is a safe instrument.
Examine frequently to find if the section is complete. When the section is completed, fasten a hook (Roser) into the eye of the tirefond, and pull gently on the disk, aiding in its removal with the elevator.
Make the sawn edge perfectly smooth.
If two walls of bone are to be sawn through, the first must be sawn with a large trephine, and the second with a much smaller one, as when trephining the frontal sinuses.
In trephining the long bones, as, for example, the head of the tibia, the small crown trephine is used.
To study trephining for depressed fracture of the skull, fracture with a hammer the skull in various localities. Expose the parts as directed. Place the point of the pin of the trephine near the margin on the solid, undepressed bone, and, if possible, away from sinuses, or the middle meningeal artery.
Select a spot where the line of fracture between two depressed fragments meets the margin. The crown of the trephine must overlap the margin of the depression. Remove the disk or portion of a disk of bone, which will allow the elevator to raise the depressed fragments. Remove all detached fragments and small fragments which have been considerably depressed. Make the bony margin smooth with the rongeur, gouges, chisels, or scoops. Saw any sharp angles of bone with Hey's saw, using the straight toothed edge for straight section, and the rounded edge for curved section.
If the wound is made with a pick, the fragments removed must be fitted together to ascertain if any pieces have been driven into the brain.
Provide for drainage from the wound, and stitch together the flaps.
OPERATION FOR STRABISMUS. Place the subject on the back. Stand facing the subject. Keep the eyelids separated by means of a stop-speculum.
Catch up the conjunctiva just external to the cornea with toothed forceps, and rotate the eye outward. An assistant, standing behind the head of the subject, must hold these forceps. This places the eye in position for operation upon the tendon of the internal rectus.
To operate upon the tendon of the external rectus, the conjunctiva is seized internally to the cornea and the globe rotated inward.
Pinch up with a pair of ordinary dissecting forceps a vertical fold of conjunctiva and sub-conjunctival tissue, at the point of intersection of the lower horizontal and the vertical tangents to the cornea. With a small pair of blunt-pointed scissors, snip this fold, cutting it down to its base, thus making a horizontal wound. This cut divides the capsule of Tenon, thus opening into the lymph-space around the sclerotic.
Still holding the forceps in the left hand, insert a strabismus-hook into the opening. Direct the end of the hook downward slightly, and then horizontally backward, half the distance on the globe toward the entrance of the optic nerve. Bring the hook upward and forward until its end bulges the conjunctiva just above the upper edge of the tendon.
In these manœuvres, the end of the instrument must be kept applied to the surface of the sclerotic.
Pull slightly upon the tendon toward the cornea. The hook is retained posterior to the corneal margin by the tendon. With the small, probe-pointed scissors curved on the flat, divide the tendon from below upward between the hook and the cornea. The lower blade of the scissors must be kept in contact with the hook, and the upper between the tendon and the conjunctiva. The curve of the scissors must follow the curve of the hook.
Search to find if any part of the tendon is undivided, which bands would prevent the hook from advancing to the corneal margin.
EXCISION OF THE EYE.
Keep the eyelids apart by means of a stop-speculum.
With a pair of toothed forceps catch hold of the conjunctiva and sub-conjunctival tissue external to the cornea. Divide these tissues all around the cornea, keeping close to the corneal margin. Draw up with a strabismus-hook the tendon of the external rectus, which is to be divided about an eighth of an inch from its attachment to the sclerotic. Grasp with forceps the stump of tendon of the external rectus left attached to the sclerotic in order to control the globe in the subsequent steps of the operation. Hook
up the tendons of the superior and inferior recti muscles, and divide them close to the sclerotic.
Pass posteriorly a pair of probe pointed scissors curved on the flat with their curve following the external surface of the globe until their point touches the optic nerve. Separate the blades of the scissors and include the nerve, which must then be divided.
The globe is now easily drawn forward, when the attachment of the oblique and internal rectus muscles and any
fibrous bands must be divided close to the sclerotic.
EXTRACTION OF TEETH.
Place the subject on the back, with a block under the head during the extraction of the lower teeth.
The head must hang over a block during the extraction of the upper teeth.
Grasp the forceps in the right hand, with the thumb laid along one bar somewhat between the two bars of the handle, to prevent a crushing force being exerted on the tooth.
Stand on the right-hand side of the table.
Lightly apply suitable forceps to the neck of the tooth. Push the sharp edges of the blades of the forceps between the gum and the tooth, until arrested by the alveolar process of the maxilla. Tighten the grasp on the tooth when the different motions for the different extractions are begun.
Upper Incisors and Canine.—To extract these, use straight forceps with blades having one groove. These teeth have conical roots, hence are loosed by slight rotation. The blades of the forceps are crowded down into the socket so as to catch hold nearer the root. To extract, pull downward and slightly forward, after the tooth has been loosened sufficiently by slight rotation.
Upper Bicuspids. — Use forceps with narrow blades, and with the handle curved to avoid coming in contact with the lower teeth. The tooth has a root which is flattened laterally. Apply the forceps; force the tooth outward and then tilt it outward and inward until loose. Crowd the forceps-blades toward the root, and extract by pulling downward.
Upper Molars. Right and left forceps are necessary. The outer blade has two grooves corresponding to the roots of the tooth. The blades make an obtuse angle with the handle. The internal edge of the alveolar process being the stronger and the palatine root liable to fracture, apply the forceps and force the tooth outward. Move the tooth from side