780 ORGANS OF VOICE AND RESPIRATION. 



is smaller, more deeply placed, and more movable than in the adult. In fat, or short-necked 

 people, or in those in whom the muscles of the neck are prominently developed, the trachea is 

 more deeply placed than in the opposite conditions. 



From these observations, it must be evident that laryngotomy is anatomically the most simple 

 operation, can most readily be performed, and should always be preferred when particular cir- 

 cumstances do not render the operation of tracheotomy absolutely necessary. The operation is 

 performed thus : The head being thrown back and steadied by an assistant, the finger is passed 

 over the front of the neck, and the crico-thyroid depression felt for. A vertical incision is then 

 made through the skin, in the middle line over this spot, and the crico-thyroid membrane is 

 divided to a sufficient extent to allow of the introduction of a large curved tube. The crico- 

 thyroid artery is the only vessel of importance crossing this space. If it should be of large size, 

 its division might produce troublesome hemorrhage. 



Fig. 430. Surgical Anatomy of Laryngo-tracheal Region, in the Infant. 



Crico -thyro, 



Crumid Cartilage. 

 Superior Thyroid vfin 



Laryngo-traclieotomy, anatomically considered, is more dangerous than tracheotomy, on 

 account of the small interspace between the cricoid cartilage and the isthmus of the thyroid 

 gland : the communicating branches between the superior thyroid veins, which cover this spot, 

 can hardly fail to be divided ; and the greatest care will not, in some cases, prevent the division 

 of part of the thyroid isthmus. If either of these structures is divided, the hemorrhage may be 

 considerable. 



Tracheotomy below the isthmus of the thyroid gland is performed thus : The head being thrown 

 back and steadied by an assistant, an incision, an inch and a half or two inches in length, is 

 made through the skin, in the median line of the neck, from a little below the cricoid cartilage, 

 to the top o"f the sternum. The anterior jugular veins should be avoided, by keeping exactly in 

 the median line; the deep fascia should then be divided, and the contiguous borders of the 

 Sterno-hyoid muscles separated from each other. A quantity of loose areolar tissue, containing 

 the inferior thyroid veins, must then be separated from the front of the trachea, with the handle 

 of the scalpel ; and when the trachea is well exposed, it should be opened by inserting the knife 

 into it, dividing two or three of its rings from below upwards. It is a matter of the greatest 

 importance to restrain, if possible, all hemorrhage before the tube is opened ; otherwise, blood 

 may pass into the trachea, and suffocate the patient. 



THE PLEURA. 



Each lung is invested, upon its external surface, by an exceedingly delicate 

 serous membrane, the Pleura, which incloses the organ as far as its root, and is 

 then reflected upon the inner surface of the thorax. The portion of the serous 

 membrane investing the surface of the lung is called the pleura pulmonalis 

 (visceral layer of pleura) ; whilst that which lines the inner surface of the 

 chest is called the pleura costalis (parietal layer of pleura). The interspace or 

 cavity between these two layers is called the cavity of the pleura. Each pleura 



