488 THE BLOOD-VASCULAR SYSTEM. 



Besides the arteries distributed to the muscles by which it is covered and to the 

 substance of the gland, the branches of the superior thyroid are the following : 



Hyoid. Superior laryngeal. 



Superficial descending branch (Sterno-mastoid). Crico-thyroid. 



The hyoid (infra-hyoid) is a small branch which runs along the lower border 

 of the os hyoides beneath the Thyro-hyoid muscle ; after supplying the muscles 

 connected to that bone, it forms an arch, by anastomosing with the vessel of the 

 opposite side. 



The superficial descending or Sterno-mastoid branch runs downward and outward 

 across the sheath of the common carotid artery, and supplies the Sterno-mastoid 

 and neighboring muscles and integument. There is frequently a separate branch 

 from the external carotid distributed to the Sterno-mastoid muscle. 



The superior laryngeal, larger than either of the preceding, accompanies the 

 internal laryngeal nerve, beneath the Thyro-hyoid muscle : it pierces the thyro- 

 hyoid membrane, and supplies the muscles, mucous membrane, and glands of the 

 larynx, anastomosing with the branch from the opposite side. 



The crico-thyroid is a small branch which runs transversely across the crico- 

 thyroid membrane, communicating with the artery of the opposite side. 



Surgical Anatomy. The superior thyroid, or one of its branches, is often divided in 

 cases of cut throat, giving rise to considerable hemorrhage. Tn such cases the artery should be 

 secured, the wound being enlarged for that purpose, if necessary. The operation may be easily 

 performed, the position of the artery being very superficial, and the only structures of importance 

 covering it being a few small veins. The operation of tying the superior thyroid artery in 

 bronchocele has been performed in numerous instances with partial or temporary success. When, 

 however, the collateral circulation between this vessel and the artery of the opposite side, and 

 the inferior thyroid, is completely re-established, the tumor usually regains its former size, and 

 hence the operation has been given up, especially as better results are obtained by other means. 

 Both thyroid arteries on the same side, and indeed all the four thyroid arteries, have been tin! 

 in enlarged thyroid. 



The position of the superficial descending branch is of importance in connection with the 

 operation of ligation of the common carotid artery. It crosses and lies on the sheath of this 

 vessel, and may chance to be wounded in opening the sheath. The position of the crico-thyroid 

 branch should be remembered, as it may prove the source of troublesome hemorrhage during 

 the operation of laryngotomy. 



The Lingual Artery (Fig. 288) arises from the external carotid between the 

 superior thyroid and facial ; it first runs obliquely upward arid inward to the great 

 cornu of the hyoid bone ; it then curves downward and forward, forming a loop 

 which is crossed by the hypoglossal nerve, and, passing beneath the Digastric and 

 Stylo-hyoid muscles, it runs horizontally forward, beneath the Hyo-glossus, and 

 finally, ascending almost perpendicularly to the tongue, turns forward on its under 

 surface as far as the tip, under the name of the ranine artery. 



Relations. Its first, or oblique, portion is superficial, being contained in the 

 same triangular space as the superior thyroid artery, resting upon the middle con- 

 strictor of the pharynx, and covered by the Platysma and fascia of the neck. Its 

 second, or curved, portion also lies upon the middle constrictor, being covered at 

 first by the tendon of the Digastric and the Stylo-hyoid muscle, and afterward by 

 the Hyo-glossus, the latter muscle separating it from the hypoglossal nerve. Its 

 third, or horizontal, portion lies between the Hyo-glossus and Genio-hyo-glossus 

 muscles. The fourth, or terminal, part, under the name of the ranine, runs along 

 the under surface of the tongue to its tip : it is very superficial, being covered 

 only by the mucous membrane, and rests on the Lingualis on the outer side of 

 the Genio-hyo-glossus. The hypoglossal nerve crosses the lingual artery, and then 

 becomes separated from it, in the second part of its course, by the Hyo-glossus 

 muscle. 



The branches of the lingual artery are the 



Hyoid. Sublingual. 



Dorsalis Linguae. Ranine. 



