e of left main
bronchus at bifurcation of trachea. The bronchoscope, S, is in the
right main bronchus, pointing in the direction of the right inferior
lobe bronchus, I. In order to cause the lip to enter the middle lobe
bronchus, M, it is necessary to drop the head so that the bronchoscope
in the trachea TT, will point properly to enable the lip of the tube
mouth to enter the middle lobe bronchus, as it is seen to have done at
ML.]

Branches of the stem bronchus in either lung are exposed, or their
respective lumina presented, by manipulation of the lip of the
bronchoscope, with movement of the head in the required direction.
Posterior branches require the head quite high. A large one in the
left stem just below the left upper-lobe bronchus is often invaded by
foreign bodies. Anterior branches require lowering the head. The
_middle-lobe bronchus_ is the largest of all anterior branches. Its
almost horizontal spur is brought into view by directing the lip of
the bronchoscope upward, and dropping the head of the patient until
the lip bears strongly on the anterior wall of the right bronchus (see
Fig. 65).

[106] CHAPTER X--INTRODUCTION OF THE ESOPHAGOSCOPE

The esophagoscope is to be passed only with ocular guidance, never
blindly with a mandrin or obturator, as was done before the
bevel-ended esophagoscope was developed. Blind introduction of the
esophagoscope is equally as dangerous as blind bouginage. It is almost
certain to cause over-riding of foreign bodies and disease. In either
condition perforation of the esophagus is possible by pushing a sharp
foreign body through the normal wall or by penetrating a wall weakened
by disease. Landmarks must be identified as reached, in order to know
the locality reached. The secretions present form sufficient
lubrication for the instrument. A clear conception of the endoscopic
anatomy, the narrowings, direction, and changes of direction of the
axis of the esophagus, are necessary. The services of a trained
assistant to place the head in the proper sequential "high-low"
positions are indispensible (Figs. 52 and 70). Introduction may be
divided into four stages.
1. Entering the right pyriform sinus.
2. Passing the cricopharyngeus.
3. Passing through the thoracic esophagus.
4. Passing through the hiatus.

The patient is placed in the Boyce position as described in Chapter
VI. As previously stated, the esophagus in its upper portion follows
the curves of the cerv