ding
this region in tracheotomy because of the danger of producing chronic
laryngeal stenosis by the reaction of these tissues to the presence of
the tracheotomic cannula.

The _trachea_ just below its entrance into the thorax deviates
slightly to the right, to allow room for the aorta. At the level of
the second costal cartilage, the third in children, it bifurcates into
the right and left main bronchi. Posteriorly the bifurcation
corresponds to about the fourth or fifth thoracic vertebra, the
trachea being elastic, and displaced by various movements. The
endoscopic appearance of the trachea is that of a tube flattened on
its posterior wall. In two locations it normally often assumes a more
or less oval outline; in the cervical region, due to pressure of the
thyroid gland; and in the intrathoracic portion just above the
bifurcation where it is crossed by the aorta. This latter flattening
is rhythmically increased with each pulsation. Under pathological
conditions, the tracheal outline may be variously altered, even to
obliteration of the lumen. The mucosa of the trachea and bronchi is
moist and glistening, whitish in circular ridges corresponding to the
cartilaginous rings, and reddish in the intervening grooves.

The right bronchus is shorter, wider, and more nearly vertical than
its fellow of the opposite side, and is practically the continuation
of the trachea, while the left bronchus might be considered as a
branch. The deviation of the right main bronchus is about 25 degrees,
and its length unbranched in the adult is about 2.5 cm. The deviation
of the left main bronchus is about 75 degrees and its adult length is
about 5 cm. The right bronchus considered as a stem, may be said to
give off three branches, the epiarterial, upper- or superior-lobe
bronchus; the middle-lobe bronchus; and the continuation downward,
called the lower- or inferior-lobe bronchus, which gives off dorsal,
ventral and lateral branches. The left main bronchus gives off first
the upper-or superior-lobe bronchus, the continuation being the
lower-or inferior-lobe bronchus, consisting of a stem with dorsal,
ventral and lateral branches.

[FIG. 44.--Tracheo-bronchial tree. LM, Left main bronchus; SL,
superior lobe bronchus; ML, middle lobe bronchus; IL, inferior lobe
bronchus.]

The septum between the right and left main bronchi, termed the carina,
is situated to the left of the midtracheal line. It is recognized
endoscopically as a short, sh