1 62 APPLIED ANATOMY. 



Laryngotomy is the opening of the cricothyroid membrane. It is rarely 

 done, but it is of service in cases of choking from obstruction of the larynx, foreign 

 bodies, etc. 



There is not sufficient room between the cricoid and thyroid cartilages to do 

 this operation properly until puberty has been reached and the larynx has enlarged. 

 The cricoid cartilage is narrow in front but wide behind. Its upper edge rises rapidly 

 as it passes backward, forming an upper crescentic border, the concavity being 

 upward. The lower edge of the thyroid is concave downward. Thus the two edges 

 make an oval opening in front which in children is too small to hold the tracheotomy 

 tube. The nearness to the vocal cords is also a serious objection. Performing a 

 laryngotomy is -the easiest and quickest way to enter the air-passages. Both the 

 thyroid and cricoid cartilages in the median line are practically subcutaneous. A lon- 

 gitudinal incision of the skin is usually advised, after which a transverse incision is em- 

 ployed for opening the cricothyroid membrane. The tube is to be shorter than the one 

 ordinarily used for tracheotomy. The cricothyroid artery, running across the mem- 

 brane, is usually too insignificant to cause any trouble ; it is nearer the thyroid cartilage, 

 therefore the cut through the membrane should be close to the cricoid cartilage. 



Tracheotomy is the opening of the trachea. There are two varieties, the 

 high and the low, according as the tube is inserted above or below the isthmus of 

 the thyroid gland. When in the adult male the neck is in line with the axis of the 

 body the lower border of the cricoid cartilage is about 4 cm. ( i ^ in. ) above the 

 sternum. When the head is tilted far back the larynx is drawn upward and the 

 lower border of the cricoid is 6 cm. (about 2^ in.) above the sternum. Hence in 

 doing a tracheotomy the head is to be tilted far back. The total length of the 

 trachea is 10 to 12 cm. (Morris, Hensman), beginning opposite the sixth cervical 

 vertebra, upper border in the child and lower in adults, and ending opposite the 

 fifth dorsal. About half of it is above and half below the top of the sternum. It is 

 composed of 14 to 20 rings. In the adult the isthmus of the thyroid gland covers 

 the second, third, and fourth rings. There are about eight rings above the sternum. 



According to Symington and Guersant (Treves) the diameter of the trachea is 

 about as follows : 



\Yz to 2 years 5 mm. 



2 to 4 years 6 mm. 



4 to 8 years 8 mm. 



8 to 12 years. 10 mm. 



12 to 15 years 12 mm. 



Adults 12-15 mm - 



A knowledge of the size of the trachea is necessary in order to select a trache- 

 otomy tube of a size suitable to the particular case. The liability is to select too 

 large a tube for young children, particularly infants. If this is done it may be very 

 difficult to introduce the tube, or the trachea may even be torn in the attempt. In 

 operating, an incision 2.5 to 3 cm. long is to be made in the median line. This 

 may cut the anterior jugular vein. If carried near to the sternum it will certainly 

 divide the communicating branch between the anterior jugulars at that point. The 

 top of the incision in a child will be over the cricoid cartilage, and as soon as the skin 

 has been divided the finger is to be inserted and the cricoid cartilage felt and recog- 

 nized. This will show how deep the trachea lies. In very young children the 

 isthmus of the thyroid gland is liable to come up to the cricoid cartilage and the dif- 

 ficulty of displacing it far enough down to allow the tube to be inserted is such that 

 it may be best to divide it. Therefore after the skin and deep fascia have been divided 

 and the cricoid recognized by the finger the soft tissues covering the trachea imme- 

 diately below the cricoid are grasped on each side with a haemostatic forceps and 

 divided between them. These tissues may embrace the isthmus of the thyroid gland, 

 the edges of the sternohyoid muscles, some veins, branches from the superior and 

 inferior thyroids, and the fascia covering the gland and overlying the trachea. 



The trachea should be cleared before opening it. A sharp hook is inserted into 

 the cricoid cartilage to steady it and an incision is made into the trachea from below 

 upward. In making this incision the utmost care must be taken not to cut through 



