1182 SURFACE AND SURGICAL ANATOMY. 
The course of the carotid vessels is indicated upon the surface by a line extending 
from the upper end of the sterno-clavicular articulation to a point midway between 
the angle of the jaw and the tip of the mastoid process; a poimt upon this line, 
at the level of the upper border of the thyroid cartilage, overlies the bifurcation 
of the common carotid. ‘The anterior belly of the omo-hyoid crosses the common 
carotid at the level of the cricoid cartilage. The pulsations of the carotid vessels 
may be felt in the hollow between the larynx and the anterior border of the sterno- 
mastoid. In the carotid triangle the external carotid lies internal and anterior 
the internal carotid. The seat of election for ligation of the external carotid 
is between its superior thyroid and lingual branches, a finger’s breadth below the 
tip of the great cornu of the hyoid bone; the difficulty in the operation is due to 
the plexus of veins (formed by the common facial, lingual, and superior thyroid 
veins) which overlies the artery. The lingual and facial arteries frequently arise 
from a common trunk which must not be mistaken for the external carotid. The 
superior thyroid artery arises opposite the upper cornu of the thyroid cartilage, which 
may be distinctly felt 1 in. helow the tip of the great cornu of the hyoid bone. 
The vessel and its companion vein are common sources of hemorrhage in cut-throat. 
The guide to the lingual artery, in the carotid triangle, is the tip of “the ereat cornu 
of the hyoid bone, above which it forms an arch, crossed by the hy poglossal nerve. 
The vessel enters the digastric triangle by passing beneath the tendons of the 
stylo-hyoid and digastric muscles. When ligation of the artery is called for, it is, 
as a rule, preferable to secure it in the carotid rather than the digastric triangle. 
From a surgical point of view the internal jugular vein is the most important 
structure in the anterior triangle. In the carotid division of the triangle it over- 
laps the carotid vessels, and its sheath les close beneath the general envelope of 
deep cervical fascia. About the level of the hyoid bone it receives the large common 
facial vein, and it is the glands in the neighbourhood of those which overlie the 
junction of this vein with the internal jugular that are most frequently the seat 
of tubercular disease, because they receive such a large number of the lymphatics 
of the head, both superficial and deep. 
The hypoglossal nerve curves forwards across the carotid vessels at the level of 
the lower border of the posterior belly of the digastric. The vagus nerve descends 
vertically behind and between the carotid vessels and the internal jugular vein ; 
care must be taken not to include it when ligaturmg the common carotid or 
internal jugular. Surgically, the spinal accessory is the most important nerve in 
the anterior triangle; it enters the substance of the sterno-mastoid muscle 1 in. 
below the tip of the mastoid process. A portion of the nerve is resected in the 
treatment of spasmodic wry-neck, and it is almost always exposed in the removal 
of the upper carotid group of deep cervical glands. The course of the nerve 
may be mapped out upon the surface by drawing a line from a point midway 
between the tip of the mastoid process and the angle of the jaw to the middle of 
the posterior border of the sterno-mastoid muscle, and thence across the posterior 
triangle to the anterior border of the trapezius, beneath which it passes at the 
level of the seventh cervical spine. The deeper guides to the nerve are the 
posterior belly of the digastric, the internal jugular vein, and the transverse 
process of the atlas, which is felt as a distinct bony landmark midway between 
the tip of the ARREST and the angle of the jaw. The cervical sympathetic hes 
in the posterior wall of the vascular compartment of the neck, and may be 
reached by an incision along the posterior border of the sterno-mastoid: the 
anterior surfaces of the roots of the transverse processes of the vertebrae are the 
deep guides to the nerve. The cervical plexus, which lies behind the upper half 
of the sterno-mastoid upon the levator anguli scapule and scalenus medius 
muscles, may be exposed through an incision along the posterior border of the 
upper half of the sterno-mastoid “muscle. The phrenic nerve, the most important 
branch of the cervical plexus, arises one inch above the carotid tubercle and 
descends almost vertically upon the scalenus anticus; it is overlapped by the 
outer margin of the internal jugular vein. 
The muscular or lower carotid triangle is an important triangular inter- 
muscular space bounded by the anterior border of the sterno-mastoid, the anterior 
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