1832 



HUMAN ANAT(3MY. 



directly in the median line, and divides skin, superficial and deep fascia, the junction 

 of the alse of the thyroid, and the mucous membrane of the larynx. 



Laryngotomy (through the crico-thyroid membrane) may be indicated in adults 

 for impending suffocation from any form of obstruction of the glottis. In children 

 the space is too small.. A median incision beginning over the thyroid cartilage is 

 carried to half an inch below the cricoid cartilage. The skin and fascice having been 

 divided, the crico-thyroid membrane is exposed between the two crico-thyroid muscles, 

 which sometimes require separation. The crico-thyroid arteries may be exception- 

 ally large, and in any e\'ent should usuallv be ligated, although in cases of great 

 emergency that step may be postponed until the membrane has been divided. This 

 may be done by a transverse incision to minimize the risk of hemorrhage. The 

 nearness of the vocal cords to the opening renders this operation unsuitable to cases 

 in which a tracheotomy tube must be worn for some time. 



Excision of the larynx, occasionally done for malignant disease, necessitates the 

 separation of the larynx from the sterno-thyroid and thyro-hyoid muscles laterally, 

 from the inferior constrictor and the hyoid bone above, from the trachea below, and 

 from the pharynx and oesophagus posteriorly. The superior and inferior thyroid arte- 

 ries, or their branches, and the superior and inferior laryngeal nerves will be divided. 



For landmarks of the neck, see page 554. 



THE SUBDIVISIONS OF THE THORAX. 



As the entire respiratory apparatus, with the exception of the larynx and a part 

 of the trachea, is within the thorax, it is advisable to describe the subdivisions of that 



Fig. 1557. 



CEsophagus- 



Innominate artery 



Left innominate vein 

 Arch of aona 



Sternum 

 Ascending aorta 



Right ventric!e_ 

 Right auricle_ 



Diaphragm 



Trachea 



-IV thoracic vertebra 



J— Right pulmonary 

 artery 



J^eft auricle 



-CEsophagus 



Jiiferior vena cava 



Liver Spigelian lobe 



Median sagittal section of formalin subject ; relative position of mediastinal spaces outlined in red. 



cavity. The lungs, enveloped in their serous coverings, the pleurae, fill the greater 

 part of the sides of the chest external to planes passing forward from the sides of the 



