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: THE NECK. 1183 
belly of the omo-hyoid and the sterno-hyoid. By making an incision along the 
left anterior border of the sterno-mastoid muscle, and passing through this triangle, 
the surgeon reaches, in order from before backwards, the internal jugular vein, the 
common carotid artery, the vagus, the thoracic duct (on the left side), the middle 
cervical ganglion of the sympathetic, the inferior thyroid artery, the vertebral vessels, 
the recurrent laryngeal nerve, and the cesophagus. The most important bony land- 
mark in this triangle is the prominent anterior tubercle of the transverse process 
of the sixth cervical vertebra. The common carotid artery may be compressed 
against this tubercle, which is therefore termed the “carotid tubercle.” As it is 
the most important cuide to the vertebral artery, which enters the foramen in its 
transverse process, it is often referred to as the “ vertebral arterial tubercle.” 
In operations in this region, on the left side, it is important to avoid the 
thoracic duct, which extends upwards into the neck 1 in. vertically above the 
inner end of the clavicle, and, after arching outwards behind the common carotid, 
descends behind the lower inch of the internal jugular vein. 
The cervical portion of the esophagus, which begins at the level of the cricoid 
cartilage, descends behind, and a little to the left of, the trachea. To expose it, the 
surgeon, after passing through the above-mentioned muscular triangle, passes 
between the trachea and the carotid sheath. In opening the cesophagus care must 
be taken not to injure the recurrent laryngeal nerve which ascends in the groove 
between it and the trachea, and also that the loose submucous cellular inter val must 
not be mistaken for the lumen of the tube. The recurrent laryngeal nerve must 
be avoided also in operations connected with the thyroid gland; it is most lable to 
be injured during the application of a hgature to the inferior thyroid artery, which 
arches inwards in front of the nerve to reach the posterior surface of the gland. 
The Posterior Triangle.—limbedded in the deep cervical fascia at the posterior 
border of the sterno-mastoid muscle, is a chain of lymphatic glands which lies in 
close relation to the branches of the cervical plexus; these glands are a frequent 
source of abscess in pediculosis and impetigo of the scalp. "The posterior belly of 
the omo-hyoid, which forms the upper boundary of the supraclavicular division of 
the posterior triangle, passes beneath the posterior border of the sterno-mastoid at 
a point about 1 in. above the clavicle. The external jugular vein, usually visible 
through the skin, runs in a line from the angle of the jaw to the middle of the 
clavicle ; it is the vessel which is generally opened to relieve the right side of the 
heart in asphyxia. The lumen of ‘the vein is kept patent where it pierces the fascia 
of the subclavian triangle; hence a wound of the vein in this situation is Hable to 
be followed by the suction of air into the circulation during inspiration. The third 
part of the subclavian artery can be compressed against the first rib by pressing 
downwards and backwards immediately above the clavicle, a little behind the 
posterior border of the sterno-mastoid muscle. To map out the cowrse of the sub- 
clavian artery in the neck, draw a line, convex upwards, from the upper border of 
the sterno-clavicular articulation to the middle of the clavicle, the highest part of 
the arch to reach from 4 to 1 in. above the bone. To ligature the vessel in the third 
part of its course, an angular incision is made along the middle of the upper border 
of the clavicle and the lower part of the posterior border of the sterno-mastoid muscle. 
The most important guides to the vessel are the posterior belly of the omo-hyoid, 
the outer border of the scalenus anticus, and the scalene tubercle of the first rib. 
The close relation of the vessel to the lowest trunk of the brachial plexus and to 
the cervical pleura must be kept in mind. In the rare instances in which a 
cervical rib is present the subclavian artery lies either in front of it, or arches 
above it, according to the degree of dev elopment of the rib. The subclavian vein 
hes below, and anterior to the ar tery, altogether under cover of the clavicle. 
Entering the posterior triangle from behind the outer border of the scalenus 
anticus are the trunks of the paecial plexus. They lie upon the scalenus medius, 
and can be felt through the skin immediately above and behind the third part on 
the subclavian artery. The carotid tubercle lies between the anterior primary 
divisions of the sixth and seventh cervical nerves. The fifth cervical nerve is that 
which suffers most when the plexus is injured by forcible extension upwards of the 
arm, such as occurs, for instance, in the “ Obstetrical Paralyses” of Duchenne. 
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