THE INFRA -HYOID REGION. 77 



from the thyroid body ; and the thyroidea iraa artery, 

 when it exists, is generally a branch of the innominata. 

 On the right side of the neck, the common carotid 

 artery crosses the lower portion of the trachea obliquely, 

 but subsequently lies parallel to it ; on the left side the 

 common carotid is deeper than on the right and lies 

 along the trachea. It must be borne in mind that 

 neither of these vessels is in actual contact with the 

 trachea. Behind the trachea is the oesophagus, which 

 commences opposite the fifth cervical vertebra and cri- 

 coid cartilage, and passes to its left side a circumstance 

 which is taken advantage of for the performance of the 

 operation of oesophagotomy. On either side is the com- 

 mon carotid artery, the nearer being the left, owing to 

 the projection of the oesophagus towards that side ; and 

 crossing it obliquely are the superior and inferior thy- 

 roid arteries. The recurrent laryngeal nerve lies in the 

 interspace between the borders of the trachea and oesoph- 

 agus, and passes below the inferior constrictor and into 

 the larynx through the crico-thyroid membrane. The 

 oesophagus is separated from the cervical spine and the 

 muscles covering it viz., the recti antici, longi colli, 

 and that portion of the deep cervical fascia which is 

 applied to their anterior surface, by a layer of very lax 

 cellular tissue, which permits of the constant gliding of 

 the oesophagus and trachea in their several movements, 

 and is, as before mentioned, frequently the seat of ab- 

 scesses. For greater convenience of reference, two tri- 

 angular spaces, termed by Velpeau the omo-hyoid and 

 the omo-tracheal, may be noted ; the former, bounded 

 by the hyoid bone above, sterno-mastoid externally, 

 and the omo-hyoid internally, contains the superior 

 thyroid artery, superior laryngeal nerve, a portion of 



