THE NECK 1355 



when the landmarks for tracheotomy are sought for in children with short fat 

 necks. 



The cricoid, on the other hand, is always to be made out. It corresponds in horizontal 

 plane to the following: — (1) The sixth cervical vertebra. (2) The junction of pharynx and 

 oesophagus : from the narrowing of the tube here, foreign bodies may lodge at this point and cause 

 dyspnoea by pressing on the air-tube in front. The cricoid is taken as the centre of the incision 

 in oesophagotomy, and also for ligature of the common carotid. (3) The junction of larynx 

 and trachea. (4) The crossing of the omo-hyoid over the common carotid. (5) The middle 

 cervical ganglion. Above the cricoid is the crico-thyreoid membrane. In laryngotomy, the 

 deepest part of the incision should be kept to the middle line for fear of injuring the crico- 

 thyreoids, and as near the cricoid as possible, so as to avoid the neighbourhood of the vocal 

 cords and the small crico-thyreoid vessels. The space is always small, and, after middle life, 

 increasingly rigid. 



The distance between the cricoid and the manubrium is only about 3.7 cm. 

 (1| in.). When the neck is stretched, about 1.8 cm. (f in.) more is gained. 

 Thus, as a rule, there are not more than seven or eight tracheal rings above the 

 sternum. Of these, the second, third, and fourth are covered by the thyreoid 

 isthmus. 



The parts met with in the middle line — (a) above, and (b) below, the isthmus — high and 

 low tracheotomy — should be borne in mind: (a) Skin, superficial fascia, branches of transverse 

 cervical and infra-mandibular nerves, lymphatics, cutaneous arteries, anterior jugular veins — 

 with their transverse branches smaller above — deep fascia, sterno-hyoids, cellular tissue, supe- 

 rior thyreoid vessels, and pre-tracheal layer of deep fascia. The importance of this last is two- 

 fold, as, first, the tube in tracheotomy may be passed between it and the trachea, and after a 

 wound in this region this layer, continuous with the pericardium, may conduct discharges into 

 the mediastina. (b) The surface structures are much the same, but the anterior jugular veins 

 and their transverse branches are much larger. The inferior thj'reoid veins are also larger. A 

 thyreoidea ima may be present, and the innominate artery, especially in children, may be 1.2 

 cm. (I in.) above the sternum. The trachea is also smaller, deeper, and less steadied by muscles. 

 The thymus, too, in young children, may prove a difficulty. Thus, in children, the high opera- 

 tion, incising the cricoid and crico-tracheal membrane, if needful, is to be preferred. The cricoid 

 is, however, not to be incised, if possible; the higher the tube is inserted, the greater the irritation. 



The suprasternal notch, between the sternal heads of the sterno-mastoids in on a level with 

 the disc between the second and third thoracic vertebrae. Just below the level of the cricoid 

 cartilage, on deep pressure at the anterior border of the sterno-mastoid the transverse process of 

 the sixth cervical vertebra may be felt. It is known as Chassaignac's carotid tubercle, and the 

 common carotid may be compressed against it. Compression below it will command the 

 vertebral artery as well. 



The thyreoid gland enclosed in a capsule of deep fascia derived from the pre- 

 tracheal layer (fig. 1070) is closely connected by this to the upper trachea and 

 larynx. The upper somewhat pointed extremity of each lateral lobe reaches to 

 the upper and back part of the thyreoid cartilage; here enter the superior thyreoid 

 vessels. The lower layer and rounded extremity reaches to the fifth or sixth 

 tracheal ring; its posterior and lower aspect is in relation to the inferior thyreoid 

 vessels and the recurrent nerve; the lateral lobe, posteriorly, also overlaps the 

 carotid sheath, which may be infiltrated in malignant disease of the thyreoid. 

 The thyreoidea ima has been mentioned above. 



The isthmus in- the adult is opposite to the second, third, and fourth tracheal rings. At 

 its upper border is an arterial arch formed by the superior thyreoids; over the anterior surface 

 of the gland and isthmus the inferior thyreoid veins take origin in a plexus. The upper border 

 of the thymus (fig. 1100) may be in relation with the lower border of the isthmus. From the 

 upper border of the latter, the pyramidal lobe, especially on the left side, is often present, reach- 

 ing by a pedicle to the hyoid. The pyramidal lobe, when present, is the persistent remnant of 

 the thyreo-glossal duct, and occasionally cystic outgrowths persist obstinately as remnants of 

 this duct, in the middle line, above, behind, and below (the commonest form) the hyoid bone. 



In short-necked people the thyreoid is relatively lower in relation to the sternum, and en- 

 largements of the gland are apt to become mainly intra-thoracic. An enlargement of the 

 thyreoid is liable to give trouble by pressure on (1) the trachea, which is compressed laterally 

 between the lateral lobes; (2) the oesophagus; (3) the internal jugular vein and carotid artery; 

 (4) the recurrent laryngeal or cervical sympathetic nerves. 



Parathyreoids. — These small glands, about the size of a pea, vary somewhat in number and 

 situation. There are usually four^two behind each lateral lobe. The upper glands lie im- 

 bedded in the capsule of the thyreoid about the junction of the middle and upper thirds of the 

 lateral lobes on the posterior aspect. The lower pair lie nearer the lower poles of the lateral 

 lobes, sometimes separated from them by a distinct interval. Excision of all the parathyreoids 

 gives rise to tetany in animals. 



The stemo-mastoid is the landmark for several important operations. Its 

 medial border, the thicker and better marked of the two, overlaps the carotids; 



