2 3 o HEAD AND NECK 



each side viz., the superior thyreoid, the middle thyreoid, 

 and the inferior thyreoid. The superior and middle thyreoid 

 veins cross the common carotid artery and join the internal 

 jugular; the inferior thyreoid vein descends on the trachea. 

 At the root of the neck it usually joins its fellow of the 

 opposite side to form a common stem which opens into the 

 left innominate, in the thorax. 



Trachea and (Esophagus. The cervical portions of the 

 windpipe and the gullet may now be studied. Both the 

 trachea and the oesophagus begin at the level of the cricoid 

 cartilage, anterior to the sixth cervical vertebra. From that 



Trachea 



Thyreoid gland 

 Recurrent nerve ^- "^"K^P*?--/ M< sternotn y reoideus 



--^>- t ' " > ^'^>3L^ ^ m " stern ohyoideus and 



Common carotid artery >^\ ^^-f^^jtSm S^^tst 1 *--- ' omohyoideus 



'Sffii^^ ^^fcClV- WL Nfcw Sterno-mastoid 

 Internal jugular vein ^^p 







Vagus nerve '" ^H, 



- ^L - "--,* >*"" '" a> "~" ^ ecurrent m 



ferior thyreoid artery ' ,- \ r >?\ ""-.Vertebral vein 



Vertebral vein 



Vertebral artery / (Esophagus ist thoracic vertebra 



Longus colli 



PIG. 83. Transverse section through the Thyreoid Gland, Trachea, and 



Gullet, at the level of the first Thoracic Vertebra. 



point they extend downwards, anterior to the vertebral 

 column, to the thoracic cavity. 



The trachea, or windpipe, is a wide tube which is kept 

 constantly patent by the cartilaginous curved bars embedded 

 in its walls. The bars do not form complete circles ; pos- 

 teriorly they are deficient, and, in consequence, the posterior 

 surface of the trachea is flattened. The trachea is con- 

 tinuous above with the larynx, and, throughout its course in 

 the neck, it is placed in the median plane of the body. The 

 anterior relations of the trachea have already been fully 

 discussed in the account of the parts which occupy the 

 middle line of the neck (p. 127). Posteriorly, it rests upon 

 the gullet. A common carotid artery and the corresponding 



