which spring from the external one, viz. the occipital passing obliquely toward the mastoid process, under cover of the posterior belly of the digastric, and hooked round by the hypo-glossal nerve; the muscular, which is not invariably present, inclining outward to the sterno-mastoideus; the lingual and facial (divided by an imaginary prolongation of the cornu of the os hyoides from the superior thyroid) entering the digastric space, the former transversely by running along the cornu of the os hyoides between the hyo-glossus and middle constrictor, the latter more obliquely ascending; and the pharyngeal artery deeply running upward beside the pharynx. To all these branches a more particular description has been given in a previous article, than would be suitable to the present one; and to that the reader is referred for the details of their distribution. (See Carotid.) The jugular vein descends externally to the internal, as to the common carotid, the vagus lying, as in the lower region of the neck, between the two vessels and rather behind them. The vein receives several branches, in traversing this triangle, from the larynx and tongue, and usually the facial vein: all these, since they come from within, must cross in front of the artery, and sometimes form an intricate plexus, which much embarrasses an operator. In front of the sheath descends, with a slight inward obliquity, the branch of the lingual nerve, which at the lower part of the space, and while lying over the vein, forms a reversed arch of communication with the cervical plexus, whence branches are distributed to the sub-hyoid muscles. The integuments and platysma require no particular notice; their veins and nerves have already been described; among the former must be reckoned the anterior jugular; the space contains a great number of lymphatic glands, a long chain of which (glundulæ concatenatæ) lies along the outer side of the sheath of the vessels, while some also lie about the thyroid and lingual arteries on the inner side of the sheath. The surgical relations of this space are chiefly confined to the arteries: ligature of the common carotid or of either of its branches may easily be performed here, since the vessels lie under a much less thickness and variety of parts than below. A vertical incision falling on the point of intersection of the omo-hyoid and sterno-mastoid muscles, and successively dividing the superficial fascia (in which the platysma and cutaneous nerves are contained) and the cervical aponeurosis (a single layer, as it stretches across the space, but, of course, double where it encloses the sterno-mastoid,) exposes the sheath of the vessels, the veins which transversely cross its arterial portion, and the descendens noni which runs on the part of its wall corresponding to the jugular vein: and here, as he might open the sheath lower or higher, the surgeon would expose the common carotid or its branches; and, in remembering that the internal (so named from its distribution only) lies at first external to and behind the other, he would be able to isolate and secure either of these at his option. In any attempt to tie the branches of the external carotid, a clear notion of their respective relations to the hyoid bone is of indispensable necessity; and, in ascending toward the digastricus, it must be remembered that the lingual nerve crosses the carotid sheath but just below the border of that muscle, and that it and the facial vein are consequently exposed to injury. Attempts at suicide by cutting the throat seldom succeed; the incision is usually made closely either above or below the hyoid bone; in the former case entering the digastric regions, and dividing, with the muscles of the tongue, the lingual and perhaps the facial artery; in the latter case, traversing the thyro-hyoid membrane, penetrating the pharynx, perhaps implicating the epiglottis, dividing the thyroid artery, and very rarely reaching the external carotid. The mode of searching for these vessels must vary according to circumstances, but, in all essential particulars, may readily be deduced from their anatomy.
4. The postero-superior triangle is a large space of singularly little interest, having its inferior boundary fixed by the omo-hyoid muscle, its anterior by the diagonal which intersects this, its posterior by the edge of the trapezius, and its apex by the mastoid process. It contains, below, a part of the brachial plexus (the anterior branches, namely, of the fifth and sixth cervical nerves, which directly pass beneath the omo-hyoid muscle into the adjoining inferior triangle,) the whole of the cervical plexus and many of its branches, the spinal accessory nerve, obliquely crossing from the sterno-mastoid to the trapezius, which it enters near its clavicular insertion, and some ramifications from the arteria transversalis colli, which, under the name of superficial cervical, ascend in the space, supply its cellular membrane and lymphatic glands, and ultimately inosculate with descending twigs from the occipital. The pre-vertebral fascia covers its deep parts; the common cervical extends between its borders; the platysma myoides exists as a covering for it only in its lower part.
5. The postero-inferior triangle, (that of the subclavian artery,) is one of manifold importance. The well-known lines of the omo-hyoid and clavicle limit its area above and below, the former dividing it from the space last considered, the latter from the pectoral region; intersecting the omo-hyoid, our imaginary diagonal, as it stretches from the centre of the sterno-clavicular joint upward and outward, bounds it internally, and constitutes an arbitrary but most useful separation between the space, exclusively appropriated to the subclavian artery with its branches and that internally adjoining it, (the antero-inferior,) which is the proper territory of the carotid. The parts forming its deep or posterior wall are, the transverse processes of the lower cervical vertebra; and head of the first rib, the outer edge of the longus colli and the broad lower part of the scalenus posticus: its inferior wall presents the upper surface of the first rib, and within the curve of this bone a part of the upper inlet of the
