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1180 SURFACE AND SURGICAL ANATOMY. 
and chin. About 1 in. below the hyoid bone is the pomum Adami, more prominent 
in the male than in the female. On either side of the pomum Adami are the ale 
of the thyroid cartilage, while between the latter and the hyoid bone is the thyro- 
hyoid membrane. In the operation of swb-hyord pharyngotomy the epiglottis and 
the superior opening of the larynx are reached by passing through the anterior 
wall of the pharynx at the level of the thyro-hyoid membrane. The structures 
divided from without inwards are: the integuments, the sterno-hyoid, omo-hyoid, 
and thyro-hyoid muscles, the middle portion of the thyro-hyoid membr: we, along 
with a layer of fat between it and the lower part of ‘the epiglottis, and, fin: ally, 
the elosso- epiglottidean ligament and fold of mucous membrane. The incision 
must not be extended too far on either side of the mesial plane for fear of 
wounding the superior laryngeal vessels and nerve which pierce the thin lateral 
portions of the thyro-hyoid membrane. 
The wound in suicidal cut-throat is generally at this level. The more important structures 
which are usually divided are: more or less of the left sterno-mastoid muscle, the superior 
thyroid vessels, the thyro-hyoid membrane, the base of the epiglottis, and, less freque utly, the 
carotid vessels, the internal jugular vein, and the superior laryngeal nerve. When the wound 
is above the hyoid bone, the lingual and facial vessels and the muscles of the tongue are the 
more important structures injured. 
At the level of the middle of the anterior border of the thyroid cartilage is the 
rima glottidis. A little more than an inch below the pomum Adami is the 
anterior arch of the cricoid cartilage, which may be readily felt, and, when the neck 
is extended, often seen; it lies a little below a point midway between the lower 
margin of the chin and the upper border of the sternum. Above the ericoid is the 
crico-thyroid membrane; in the operation of laryngotomy only the middle portion 
of the membrane is divided, in order to avoid injury to the crico-thyroid muscles. 
The small erico-thyroid branch of the superior thyroid artery lies close to the 
lower border of the thyroid cartilage. Below the cricoid cartilage is the trachea, 
which recedes as it descends, so that it lies 14 in. from the surface at the level of 
the upper border of the sternum. The isthmus of the thyroid gland hes in front of 
the second, third, and fourth rings of the trachea (Fig. 789); not infrequently, 
however, it reac shes up to the cricoid. Immediately in front of the trachea, below 
the isthmus of the thyroid, is the pretracheal fat, contaming one or two iymphatie 
glands and the inferior thyroid veins, each represented by one or more branches which 
converge as they descend. In the adult the innominate artery crosses the front of 
the trachea at the level of the upper border of the sternum: in the child, how- 
ever, it not infrequently crosses half an inch higher, a relation which must be 
remembered in performing the operation of low tracheotomy. 
In the operation of high tracheotomy the upper three rings of the trachea are divided. 
The incision, which should be mesial, divides the integuments, the tributaries of the 
anterior jugular veins, the general envelope of deep cervical fascia, and, after passing 
between the depressor muscles of the hyoid bone, the pretracheal fascia, which descends 
from the cricoid to enclose the isthmus of the thyroid gland. By dividing this fascia 
transversely below the cricoid, the isthmus may be pulled downwards and the upper rings 
of the trachea exposed. In some cases it is necessary either to divide the isthmus or to 
extend the incision upwards through the cricoid cartilage. In opening the trachea, the 
edge of the knife should be directed upwards so as to avoid injuring the vessels at the 
upper border of the isthmus. The anterior jugular veins are in danger of being woundea 
if the skin incision is not strictly mesial. In low tracheotomy the trachea “below the 
isthmus is opened; it is a more troublesome operation on account of the depth of the 
trachea and the presence in front of it of the large inferior thyroid veins and of the trans- 
verse anterior jugular vein. In children the difficulty is increased by the higher position 
of the innominate artery and left innominate vein, by the presence of the thymus oland, 
and by the shortness of ‘the neck. 
2 
Triangles of the Neck. —The lateral aspect of the neck may be divided into 
an anterior and a posterior triangle by the sterno-mastoid muscle; the former 
is further subdivided into digastric, car otid, and muscular triangles by the digastric 
and omo-hyoid muscles. The posterior triangle is subdivided into occipital and 
clavieular portions by the posterior belly of the omo- hyoid. 
