The contents of the larger posterior cervical triangle, formed by B, the sterno-mastoid before; 9, the splenius; and 8, the trapezius behind, and by the clavicle below, are the following mentioned structures--viz., A, the subclavian artery, in the third part of its course, as it emerges from behind N, the scalenus anticus; L, the transversalis colli artery, a branch of the thyroid axis, which will be found to cross the subclavian vessel at this region; I, the brachial plexus of nerves, which lie external to and above the vessel; H, the external jugular vein, which sometimes, in conjunction with a plexus of veins coming from behind the trapezius muscle, entirely conceals the artery; M, the posterior scapular artery, a branch of the subclavian, given off from the vessel after it has passed from behind the scalenus muscle; O, numerous lymphatic glands; P, superficial descending branches of the cervical plexus of nerves; and Q, ascending superficial branches of the same plexus. All these structures, except some of the lymphatic glands, are concealed by the platysma myoides A, as seen in Plate 3, and beneath this by the cervical fascia, which latter shall be hereafter more clearly represented. In somewhat the same mode as the posterior half of the omo-hyoid subdivides the larger posterior triangle into two of lesser dimensions, the anterior half of the same muscle divides the anterior triangle into two of smaller capacity. The great anterior triangle, which is marked as that space inclosed within the points, 6, the top of the sternum, the mental symphysis and the angle of the maxilla; and whose sides are marked by the median line of the neck before, the sterno-mastoid behind, and the ramus of the jaw above, contains C, the common carotid artery, becoming superficial from beneath the sterno-mastoid muscle, and dividing into E, the internal carotid, and D, the external carotid. The anterior jugular vein, 3, also occupies this region below; while some venous branches, which join the external and internal jugular veins, traverse it in all directions, and present obstacles to the operator from their meshy plexiform arrangement yielding, when divided, a profuse haemorrhage.