78 SURGICAL ANATOMY OF 



the middle and inferior constrictors, alee of thyroid car- 

 tilage, and thyro-hyoid membrane ; the latter is bounded 

 above and externally by the omo-hyoid, below and ex- 

 ternally by the sterno-mastoid, and internally by the 

 middle line of the neck, and contains the sterno-hyoid 

 and thyroid muscles, a lobe of the thyroid body, the 

 superior and inferior thyroid arteries, descendens and 

 communicans noni nerves, sides of cricoid cartilage and 

 trachea, the recurrent laryngeal nerves, and, on the left 

 side, the oesophagus. 



The superior thyroid artery arises from the external 

 carotid artery, opposite the greater cornu of the hyoid 

 bone, and at first lies superficially, in a space bounded 

 by the sterno-mastoid, digastric, and omo-hyoid mus- 

 cles. It then passes upwards and inwards, and arches 

 down to the upper part of the lobe of the thyroid body, 

 lying below the omo-hyoid, sterno-hyoid, and sterno- 

 thyroid muscles, having behind it the superior laryn- 

 geal nerve. Its crico-thyroid branch runs transversely 

 across the thyro-hyoid membrane, and may be wounded 

 in laryngotomy. 



The inferior thyroid artery, in this region, passes ob- 

 liquely upwards and inwards, crossing behind the com- 

 mon carotid artery, internal jugular vein, pneumo- 

 gastric, and sympathetic nerves ; and on the left side it 

 lies in front of the oesophagus and behind the thoracic 

 duct, and enters the lower part of the lobe of the thy- 

 roid body. These vessels very freely anastomose with 

 each other, and with those on the opposite side. The 

 superior laryngeal nerve lies deep down in this region, 

 passing behind the external and internal carotids, and 

 divides into two branches an external, supplied to the 

 crico-thyroid muscle, and a deep one, penetrating the 



