The sheath of the vessel is then to be cautiously opened to the extent of about half an inch. The internal jugular vein, possibly much distended, may overlap the artery on its outer side, and will require to be pressed, emptied, and held out of the way. A small portion of the artery being thoroughly separated from the sheath, the aneurism-needle must be passed from without inwards to avoid the vein, and keep as close to the artery as possible to avoid the vagus. The tendon of the omohyoid muscle, or, in muscular subjects, a portion of its anterior fleshy belly, may be seen crossing the vessel from above downwards and outwards at the lower angle of the wound. An enlarged lymphatic gland has occasionally given much trouble, by being mistaken for the vessel and cleaned, while the ligature has even been placed on a carefully isolated fasciculus of muscular fibres. LIGATURE OF CAROTID BELOW THE OMOHYOID.--An incision in precisely the same direction as the former, but at a slightly lower level, is required, but the dissection is rather more difficult. The edge of the sterno-mastoid when exposed must be drawn outwards; the sterno-hyoid and thyroid inwards; the omohyoid upwards; the sheath opened, and the descendens noni or its branches drawn to the tracheal side. The jugular vein and vagus are both at the outer side, and must be avoided, while the inferior thyroid artery and sympathetic nerve both lie behind the vessel, and may be included in the ligature if care be not taken. VARIETIES.--_Sedillot's Operation._--To secure the artery still lower in the neck: An incision two and a half inches long, from the inner end of the clavicle obliquely upwards and outwards in the interval between the sternal and clavicular attachments of the sterno-mastoid; this divides the superficial textures; the two portions of muscle must then be drawn apart. The internal jugular vein lies in the interval, and must be drawn to the outside before the artery can be seen at all, and it is this that makes this operation very difficult and dangerous, especially on the left side, where the vein is close to the artery, and probably even crossing it from left to right. The thoracic duct is behind. _Malgaigne's modification of the above_ is an improvement: to expose the external attachment of the muscle, to cut it through and turn it to the outside, as in the operation for ligature of the innominate, then to divide or pull inwards sterno-hyoid and sterno-thyroid, thus exposing the sheath. The needle must be passed from without inwards.