ANTERIOR BRANCHES.-iSt. The superior thyroid artery (A. thyroidea superior ) gene rally arises opposite the comu of the os hyoides a few lines above the bifurcation of the primi tive carotid ; in some rare cases it comes from the trunk of the primitive carotid : it has been also seen to arise from thelingual. It takes a tortuous course downwards and forwards, and passing under the omo-hyoid, sterno-thyroid, and sterno-hyoid muscles, arrives at the supe rior and external part of the thyroid body to which it is chiefly distributed : at first it is superficial, being covered by the integuments, platysma, cervical fascia, some lymphatic glands and small veins coming from the superior part of the larynx to Join the internal jugular ; it is also crossed by the branch of the nervus de scendens noni which is sent to the superior belly of the omo-hyoid muscle, and the supe rior laryngeal and several filaments from the sympathetic nerves to the larynx, &c. lie be neath it. In its course the superior thyroid artery, besides furnishing a variable number of smaller branches, to the muscles and other parts in its vicinity, generally gives off the three following: a. The hyoidean branch, which runs along the inferior border of the os hyoides between the hyo-thyroid muscle and the mem brane of the same name, to both which it gives branches; it inosculates with the corresponding artery of the opposite side in the mesial line, and with the lingual by a twig which passes up on the front of the body of the os hyoides. The hyoidean branch is often absent. b. The supeijicial branch passes downwards and out wards over the sheath of the carotid artery to the sterno-mastoid muscle, to which and the neighbouring lymphatic glands and integu ments it is finally distributed, anastornosing in the substance of the sterno-mastoid with branches coming from the occipital above and others from the thyroid axis inferiorly. c. The laryngeal often arising from the external carotid, an occurrence which, according to Meckel, takes place in one case in eight, passes into the larynx through the hyo-thyroid membrane, sometimes through a hole in the thyroid carti lage ; it usually accompanies the superior laryngeal nerve : its branches are lost in the internal muscles and mucous membrane of the larynx and the epiglottis. Before it enters the larynx it gives branches, some of which ascend to anastomose with the hyoidean, others de scend to the thyroid body ; one of these latter is remarkable for running across the front of the crico-thyroid membrane to anastomose with a similar branch from the opposite side ; it generally lies in the situation in whiclt laryn gotomy is performed. Having given off the
above-mentioned branches, and arrived at the superior extremity of the thyroid body, the thyroid artery divides into two branches, one of which descends along its external edge, sending off numerous branches which are lost in its substance, anastomosing freely with the inferior thyroid, the other branch descends coursing along the superior border of that body on which it expends its branches, and arriving at the mesial line below the cricoid cartilage, anastomoses with the corresponding artery from the opposite side : occasionally this brarch supplies the small artery which crosses the crico-thyroid membrane.
2. The Lingual Artery ( A. lingualis) arises after the thyroid, and sometimes, but rarely, from a common trunk with the thyroid, comes at other times and not unfrequently from the facial. This artery forms in its course a con siderable curve, the convexity of which is upwards ; it passes forwards and inwards above the comu of the os hyoides, between the mid dle constrictor of the pharynx and hyo-glossus, and mounts up towards the base of the tongue, between the hyo-glossus and sublingual gland which lie to its outer side, and the genio-glossus vvhich is internal to it ; then taking a horizontal direction, it passes forwards under the name of ranine artery, in company with the hypo-glossal nerve, coursing between the genio-glossus and lingualis muscles, as far as the point of the tongue where it anastomoses with its fellow of the opposite side. After its origin and before it passes under the posterior edge of the hyo glossus muscle, this artery runs superficially be neath the common coverings of the neck, lying on the middle constrictor of the pharynx above the cornu of the os hyoides ; superior to it lie the tendon of the digastric muscle, the stylo hyoid muscle and the hypo-glossal nerve, which after sending a filament across it to the hyo-thyroid muscle, continues its course for wards on the cutaneous surface of the hyo glossus muscle which separates the lingual nerve and artery in this part of their course.