THE SUPERIOR THYROID AND LINGUAL ARTERIES. 395 



piercing the thyro-hyoid membrane. On reaching the interior of the larynx, it 

 ramifies in the muscles, the glands, and the mucous membrane of that organ. 



(d) The crico-thyroid (vi), a small branch which crosses the membrane in the 

 interval between the thyroid and cricoid cartilages, and forms an arch with the 

 branch of the opposite side. It supplies the crico-thyroid muscle, and gives twigs 

 through the crico-thyroid membrane to the interior of the larynx. This vessel may 

 be a source of haemorrhage in the operation of laryngotomy. 



Varieties. Size. The superior thyroid artery is frequently larger or smaller than usual. 

 In either case the deviation from the accustomed size is accompanied by an opposite alteration 

 in other thyroid arteries. It has been seen extremely small, ending 1 in branches to the sterno- 

 mastoid muscle and the larynx : total absence on one side has also been recorded. (See the 

 observations on the inferior thyroid artery.) 



Origin. The superior thyroid is often transferred to the upper part of the common carotid 

 artery ; and it is occasionally conjoined with the lingual branch, or with that and the facial 

 branch of the external carotid. 



There are sometimes two superior thyroid arteries. 



Branches. The hyold branch is frequently very small, or absent. The larytigeal branch 

 often arises directly from the external carotid artery, rarely from the common carotid. 



Fig. 338. RAMIFICATION OP THE SUPERIOR THYROID 

 ARTERY. (Modified from Streckeisen.) (GK D. T.) 



*, on the cricoid cartilage, occasional branch to isthmus 

 of thyroid body ; t, an accessory tliyroid gland, resting on 

 the thyroid cartilage. 



Examples have occurred of this branch being of very 

 large size, and terminating in the thyroid body. The 

 laryngeal artery occasionally enters the larynx through 

 a foramen in the thyroid cartilage, and it has also 

 been observed to pass inwards below the cartilage. 

 The crico-thyroid artery is sometimes of considerable 

 size. A large branch often descends over the crico- 

 thyroid membrane and the cricoid cartilage to the 

 isthmus of the thyroid body (fig. 338). (A. Streckeisen, 

 on the thyroid arteries in " Beitrage zur Morphologic 

 der Schilddriise," Virchow's Archiv, ciii, 1886.) 



2. Lingual artery (iv). The lingual artery (fig. 341, p. 402) arises from the 

 fore part of the external carotid, between the superior thyroid and facial arteries, 

 and generally opposite the great cornu of the hyoid bone. From its origin it first 

 ascends for a short distance, and then bends sharply downwards, forming a loop 

 which is crossed by the hypoglossal nerve. Disappearing beneath the digastric and 

 stylo-hyoid muscles, it proceeds forwards along the upper border of the great cornu 

 of the hyoid bone, and under cover of the hyo-glossus, to near the anterior border 

 of that muscle ; it there ascends almost perpendicularly to the under surface of the 

 tongue, along which it is continued forwards to the tip, receiving the name of the 

 ranine artery. The lingual artery lies upon the middle constrictor of the pharynx 

 and the genio-glossus muscle ; and the hypoglossal nerve, which courses forwards 

 on the outer surface of the hyo-glossus, is placed above the level of the artery, 

 except at the anterior border of the muscle, where the artery ascends and issues 

 above the position of the nerve. 



Branches. (a) The hyoid branch runs along the upper border of the hyoid 

 bone, and supplies the contiguous muscles and skin, anastomosing with the artery of 

 the opposite side, and with the hyoid branch of the superior thyroid artery. 



(5) The dorsal artery of the tongue arises beneath the hyo-glossus muscle, and 

 ascends to supply the mucous membrane of the dorsum, and the substance of the 

 tongue, as well as the tonsil, ramifying as far back as the epiglottis, and communi- 



